Table of contents

Laser ablation encompasses a wide range of delicate to extreme light interactions with matter that present considerably challenging problems for scientists to study and understand. At the same time, laser ablation also represents a basic process of significant commercial importance in laser material processing—defining a multi-billion dollar industry today. These topics were widely addressed at the 8th International Conference on Laser Ablation (COLA), held in Banff, Canada on 11–16 September 2005. The meeting took place amongst the majestic and natural beauty of the Canadian Rocky Mountains at The Banff Centre, where delegates enjoyed many inspiring presentations and discussions in a unique campus learning environment.

The conference brought together world leading scientists, students and industry representatives to examine the basic science of laser ablation and improve our understanding of the many physical, chemical and/or biological processes driven by the laser. The multi-disciplinary research presented at the meeting underlies some of our most important trends at the forefront of science and technology today that are represented in the papers collected in this volume. Here you will find new processes that are producing novel types of nanostructures and nano-materials with unusual and promising properties. Laser processes are described for delicately manipulating living cells or modifying their internal structure with unprecedented degrees of control and precision. Learn about short-pulse lasers that are driving extreme physical processes on record-fast time scales and opening new directions from material processing applications. The conference papers further highlight forefront application areas in pulsed laser deposition, nanoscience, analytical methods, materials, and microprocessing applications.

Laser ablation continues to grow and evolve, touching forefront areas in science and driving new technological trends in laser processing applications. Please enjoy the collection of papers in this proceeding. Also, please join us for COLA 2007, to be held in the Canary Islands, Spain (http://www.io.csic.es/cola07/index.php).

Conference on Laser Ablation (COLA'05)

September 11–16, 2005 Banff, Canada

Supported by

Sponsors

Sponsorship from the following companies is gratefully acknowledged and appreciated

International Steering Committee

Local Organizing Committee

The dynamics of ultrafast laser ablation have been studied by pump-probe experiments, monitoring the ablated ions by time-of-flight mass spectroscopy. For both dielectric and metal target materials, despite their substantial physical difference, a rather similar, general dependence of the ion yield on the pump-probe delay has been observed: for short delays, the typical "coherence" peak occurs, then the signal goes down to zero, and after a longer delay, the signal increases again. This behaviour is discussed in a picture of energy and phase relaxation (T₁, T₂) mechanisms.

We present here the experimental and theoretical studies of drastic transformations induced by a single powerful femtosecond laser pulse tightly focused inside a transparent dielectric, that lead to void formation in the bulk. We show that the laser pulse energy absorbed within a volume of less than 1μm³ creates the conditions with pressure and temperature range comparable to that formed by an exploding nuclear bomb. At the laser intensity above 6 × 10¹² W/cm² the material within this volume is rapidly atomized, ionized, and converted into a tiny super-hot cloud of expanding plasma. The expanding plasma generates strong shock and rarefaction waves which result in the formation of a void. Our modelling indicates that unique states of matter can be created using a standard table-top laser in well-controlled laboratory conditions. This state of matter has temperatures ≈10⁵ K, heating rate up to the 10¹⁸ K/s, and pressure more than 100 times the strength of any solid. The laser-affected sites in the bulk were detected ("read") by generation of white continuum using probe femtosecond pulses at much lower laser intensity of 10¹⁰ W/cm² − 10¹¹ W/cm². Post-examination of voids with an electron microscope revealed a typical size of the void ranges from 200 to 500 nm. These studies will find application for the design of 3D optical memory devices and for formation of photonic band-gap crystals.

The evolution of the diffraction profiles during the fast thermoelastic deformation and structural transformations induced in a thin Ni film by short pulse laser irradiation is investigated in molecular dynamics simulations. Fast disappearance of the diffraction peaks characteristic for the initial crystal structure is related to the homogeneous nucleation and growth of liquid regions inside the overheated crystal. Transient thermoelastic deformation of the film prior to melting is reflected in shifts and splittings of the diffraction peaks, providing an opportunity for experimental probing of the ultrafast deformations.

The aim of the current work is the transfer of multilayer design knowledge on the Pulsed Laser Deposition (PLD) technique for industrially-scaled room-temperature growth of titanium–titanium nitride (Ti–TiN) structures. Because almost all PVD and CVD coating techniques require substrate temperatures >200°C for sufficiently adhering and dense coatings, there is high demand for the development of large-area and high-rate low-temperature vacuum deposition process like the PLD, e.g. for the coating of temperature-sensitive or shape-distortion-sensitive materials and substrates. A pulsed Nd:YAG laser (wavelength: 1064 nm) was used for depositing alternately Ti and TiN layers in Ar and N₂ atmosphere, resp., forming nearly particulate-free, very smooth and dense 1 μm thick coatings. Starting from single layers, in multilayers with thicker individual layers hardness and scratch resistance (critical load in scratch tests) is decreased, but this trend is reversed in multilayers of very thin (<100 nm) individual layers. In contrast, the compressive growth stress is dropping down continuously in the multilayers of increasing period numbers.

Increasingly requirements on the thin film quality of functionalized materials are efficiently met by a novel laser processing technique – Matrix Assisted Pulsed Laser Evaporation (MAPLE). Examples of deposition conditions and main features characteristic to film growth rate of MAPLE-fabricated organic materials are summarized. MAPLE experimental results are compared with ones corresponding to the classical Pulsed Laser Deposition (PLD). In particular, the results of investigation of MAPLE-deposited fibrinogen blood protein thin films using a KrF* excimer laser and characterized by FTIR and Raman spectrometry are reported.

Excimer lasers provide the shortest commercially available wavelengths and correspondingly, the highest commercially, available photon energies for laser material processing. Depending on the laser gas the emission of excimer lasers covers a range of wavelengths from 351 nm down to 157 nm with the respective photon energies between 3,5 eV up to 7,9 eV. In conjunction with the high ultraviolet output energies of up to 1200 mJ per pulse, excimer laser ablation offers maximum flexibility in terms of the target material spectrum and the ablation area. Process stability and thin film quality in Pulsed Laser Deposition (PLD) experiments largely benefit from the exceptional pulse-to-pulse stability of the excimer laser radiation which is of the order of 0.5 % (1 sigma). The top-hat beam profile which is imaged on the sample minimizes fractionation during the ablation process and supports stoichiometric transfer from target to substrat enabling controlled thin film growth.

We have demonstrated the high performance of UV laser microdrilling in polymers. For instance hole diameter ∼30 μm and length up to 18 mm (aspect ratio 600) can be obtained for PET when the laser beam setup is finely adjusted. In this work we further present a model for the incident laser beam which includes the optical setup and the laser source parameters (power and divergence). We show that the final hole geometry can be expressed in term of the laser source characteristics and that the optical setup composed of 2 lenses (condenser and projector) and a circular mask has to match some of the features of the source. Provided this condition is fulfilled the way to better drilling performances is outlined and will serve of guidelines for future experiments. In particular low divergence laser source can be used for smaller diameter hole or deeper drilling. This means also that the optical setup used to pattern the laser beam must be specially designed and adjusted.

Laser cladding processing with metal powder feeding has been experimented on carbon steel with VERSAlloy^TM. A special device for the metal powder feeding was designed and manufactured. By adopting proper cladding parameters, good clad layers and sound metallurgical bonding with the base metal were obtained. Analysis indicates that the micro hardness of clad layer and the heat-affected zone increased with increasing of cladding speed. The experimental results showed that VERSAlloy^TM cladded well with carbon steel.

Surface nitridation of a titanium target by the irradiation of YAG laser pulses in liquid nitrogen is reported, in comparison with that in pure N₂ gas and the gas mixture of N₂ and O₂. The atomic composition, the morphology, the color, and the roughness of the irradiated surface were examined. In the gas-phase treatment, the titanium target surface was nitrided with increasing the partial pressure of N₂. The surface treated in pure N₂ gas had a silver color and the highest N atom concentration. The surface color changed from silver to yellow or brown with the increase in the partial pressure of O₂. The depth of the nitrided layer was estimated to be several hundreds of nanometers. In contrast, the surface irradiated in liquid nitrogen had a white yellow color, and the nitrided layer was concentrated within several nanometers from the top of the surface.

The early stage of the ablation plume formation and the following dynamics of the plume expansion are studied numerically using a combination of molecular dynamics and the direct simulation Monte Carlo methods. The direct cluster ejection from the target and the following cluster-monomer and cluster-cluster collisions are considered. The presence of the ablated clusters is shown to strongly affect the dynamics of the plume expansion, leading to considerable modifications of the plume structure. Plume segregation into two components observed in the simulations is in a good qualitative agreement with the results of recent plume emission measurements.

Pulsed laser annealing was used to modify surface morphology and to enhance crystallization of amorphous films of the p-type perovskite SrFe_yCo_1-yO_2.5+x (y=0.5). The films were prepared by the pulsed laser deposition technique on sapphire substrates. Both film deposition and film annealing was done using a KrF excimer laser (wavelength = 248 nm). The effects of laser energy and pulse number on film morphology, structure and gas-sensing properties were investigated. An amorphous film did not show any sensor response to oxygen composition changes, while the same film after 80 pulses of annealing at 100mJ/cm² showed a fast response at 300°C and 400°C. In comparison to a dense crystalline film deposited at 700°C, the annealed film showed a faster response to oxygen composition changes at 300°C.

Laser interaction with nanoscale particles is distinct and different from laser-bulk material interaction, where a hot plasma is normally created. Here, we review our studies on 193 nm laser ablation of various nanoscale particles including NaCl, soot, polystyrene, and gold. The 20 ns laser beam with fluences up to 0.3 J/cm² irradiates nanoparticles in a gas stream at laser repetition rates from 10 to 100 Hz. The particle size distributions before and after irradiation are measured with a scanning mobility particle sizer (SMPS), and particle morphology is examined with electron microscopy. All the nanomaterials studied exhibit a similar disintegration pattern and similar particle formation characteristics. No broadband emission associated with particle heating or optical breakdown is observed. The nanoparticles formed after irradiation have a smaller mean diameter and an order of magnitude higher number concentration with a more spherical shape compared to the original particles. We use the photon-atom ratio (PAR) to interpret the laser-particle interaction energetics.

We visualized the density distributions of C₂ (plume), NO (ambient gas), and CN (reaction product) when a graphite target was ablated by irradiating YAG laser pulses at wavelengths of 1064 and 355 nm in ambient gas mixture of NO and He. It has been shown by the density distributions of C₂ and NO that the expansion of the plume removes the ambient gas and the plume and the ambient gas locate exclusively in both the cases at 1064 and 355 nm. A high CN density was observed at the interface between the plume and the ambient gas at 1064 nm, which is reasonable since chemical reactions between the plume and the ambient gas may occur only at their interface. On the other hand, in the case at 355 nm, we observed considerable CN inside the plume, indicating that the chemical reaction processes in the laser ablation at 355 nm is different from that expected from the density distributions of the plume and the ambient gas.

Pulsed laser irradiation in near field is one of effective ways to break optical diffraction limit for surface nano-structuring. Femtosecond laser (400 nm, 100 fs) irradiation through near-field scanning optical microscopy for sub-50 nm resolution is studied. Application of transparent particles' mask by the self-assembly for nano-hole array fabrication is also investigated. It is attributed to light enhancement in near field through the particles.

Using molecular-dynamics computer simulation, we study the materials processes in ultrathin metal films induced by ultrafast laser irradiation. We investigate four different metals (Al, Cu, Ti, W), which vary widely in their cohesive energy, melting temperature, bulk modulus, and crystal structure. Despite these variations, we find that the same materials processes are induced in these films: With increasing laser fluence, the film melts, voids are formed, the film tears (spallation), and finally fragments to form a multitude of clusters. When the energy transfer starting the process is scaled to the cohesive energy of the material, the thresholds of these processes adopt similar – but not identical – values.

We successfully achieved the poly-crystallized coatings of bio-active hydroxyapatite on titanium plates. We used several ceramic HAp targets sintered at a temperature of 500°C, 700°C, 900°C and 1100°C, and irradiation by KrF excimer laser at a fluence of about 4J/cm². The depositions were performed under 1Torr H₂O atmosphere at room temperature. In this condition, a poly-crystallized HAp layer was formed only using a target sintered at 900°C. We estimated the charged fragments from these targets by a simple ion-probe collection and found that the energy distribution of charged fragments depended on the densities of the targets.

The article deals with MAPLD deposition of thin organic layers of acetylacetonates and polypyrrole. The chemical changes of acetylacetonates during deposition were characterized by their FTIR spectra and morphology by SEM portraits. All of the deposited layers were utilised for gas detection. The measurements of sensitivity of deposited systems to hydrogen, ozone, nitrogen dioxide and water vapour were done. The hydrogen sensitivity of sensors prepared from SnAcAc was found about S=20 (1000 ppm in clear air) at region 250-300°C (sensor temperature). Highest response S = 35 to 100 ppb of ozone was achieved at low temperature (below 150°C). The maximum response S = 10 to nitrogen dioxide (1 ppm) at 250°C was measured. Polypyrrolic sensors were exposed to ozone, their sensitivity was S = 2 (100 ppb) achieved at very low temperature (25°C). It was found sensitivity to water present both as a vapour in atmosphere or contained in active layer.

We have demonstrated micromachining of bulk 3C silicon carbide (3C- SiC) wafers by employing 1028nm wavelength femtosecond laser pulses of energy less than 10 nJ directly from a femtosecond laser oscillator, thus eliminating the need for an amplified system and increasing the micromachining speed by more than four orders of magnitude.

Pulsed laser deposition (PLD) of drug nanoparticles for pharmaceutical preparation was investigated. Indomethacin (IM) was preliminary mixed with magnesium stearate (StMg) to prepare a target for PLD. By using the composite targets, the percentage of deposited nanoparticles in the collected powder increased compared to when only IM was ablated. The percentage of IM nanoparticles was the highest when IM and StMg were mixed at 1:1 ratio. Nanoparticles of the composite target were deposited on the micron sized particulate excipient, i.e., SiO₂, potato starch, and lactose. The excipient powders were mixed by rotation. Their surface coverage was evaluated by FE-SEM observation and diffuse reflectance (DR) UV-Vis spectroscopy. The surface coverage was estimated to be around 50 % for 20 min deposition time. Simple rotation of the excipient powders was found to be one of the effective methods for uniform deposition of nanoparticles.

Silk fibroin (SF) thin films were prepared by pulsed IR laser deposition. Size variation of the smallest protein units (SPU) in the films were evaluated by atomic force microscopy. Average SPU size doubled with increasing the background gas pressure by an order of magnitude. The size of SPU was significantly larger when the film was deposited in Ar atmosphere than in He while the pressure was kept constant at 100Pa. We discussed about the growth of SPU in terms of ionization as a consequence of hydrogen bond rupture by laser irradiation, with the aid of infrared spectra. Effects of the background gas were suspected primarily to be the difference in the states of collision with the fragmented protein units immediately after the laser bombardment of the target, within or near the plume zone. The results suggest the possibility of controlling the nano-structures of the protein thin film by optimizing the background gas condition.

After depositing silk fibroin (SF) thin films by pulsed IR-laser deposition, extraordinarily large particulate units up to several micrometers were observed. They include debris from the target and severely agglomerated protein units. Occurrence of those large particles was found to be minimum on the vertical substrate. We tried to eliminate large particulate units by two post-treatment operations, i.e. dry gaseous blow-off (GBO) and rinsing in water under simultaneous ultrasonication (WSU). Change in the surface structure by these post-treatments was observed by optical and electron microscopes with varying area from 1mm square down to 1μm square. GBO turned out to be suitable to eliminate the lightly attached particulates of 1-10μm, mostly those pulled out from the target while preserving morphological and chemical properties of smallest units underneath. WSU, on the other hand, pelt off more strongly attached surface irregularities. However, morphological change with an increase in the surface roughness in the range of 1nm was also observed after WSU. The latter might be associated with possible sonochemical effects.

Ultrafast laser ablation of fused silica is studied using molecular dynamics simulations. Ionization and generation of free electrons, absorption of the laser energy by free electrons and energy coupling between free electrons and ions are considered. The BKS potential is used to describe molecular interactions and is modified to include the effect of free electrons. Temperature, density, and material removal are computed, and the thermal and non-thermal mechanisms of ultrafast laser ablation of fused silica are discussed.

The effects of laser radiation induced by a sequence of ultrashort (130 fs), near-infrared (800 nm) Ti:sapphire laser pulses in ∼1 μm thick triazenepolymer films on glass substrates have been investigated by means of in-situ real-time reflectivity measurements featuring a ps-resolution streak camera and a ns-resolution photodiode set-up. The polymer films show incubation effects when each laser pulse in the sequence has a fluence below the single-pulse damage threshold. Non-damage conditions are maintained for several incubation pulses such that the reflectivity of the film shows a rapid decrease of up to 30% within 1 ns but subsequently recovers to its initial value on a ms timescale. Additional pulses lead to a permanent film damage. The critical number of laser pulses needed to generate a permanent damage of the film has been studied as a function of the laser fluence. Once damage is created, further laser pulses cause a partial removal of the film material from the glass substrate. Scanning force microscopy has been used to characterise ex-situ the irradiated surface areas. Based on these complementary measurements possible incubation mechanisms are discussed.

A low energy and high repetition rate infrared femtosecond laser system was developed for direct trace elements analysis by laser ablation/ICPMS. This system provides improved analytical performances in terms of limits of detection, repeatability, elemental fractionation and depth profile analysis in comparison to conventional nanosecond UV laser ablation used so far in analytical chemistry. Preliminary results show that limits of detection are improved by more than one order of magnitude and the elemental fractionation reduced to negligible values. In addition, depth profile resolution better than 20 nm are easily achievable on a Cr-Ni multilayer material which opens new fields of application in surface analysis.

In this paper, laser ablation is presented as a versatile technology that can be used for the fabrication of all building blocks and functional elements required for an optical interconnection, integrated in printed circuit boards (PCBs). The integration of optical interconnections in PCBs is an emerging field in which interest worldwide is rapidly growing. The limiting factor is mainly the compatibility of new technologies, used to define and fabricate the optical interconnections, with standard FR4-processing steps, temperatures and lamination pressures. Laser ablation, which is currently frequently used for the drilling of electrical micro-vias in PCBs, has proven to be fully compatible with standard PCB manufacturing. An optical two layer structure is studied that can make full use of the functionalities of 2D elements such as VCSEL or photodiode arrays.

We discuss the preparation of thin films of ferromagnetic shape-memory Ni-Mn-Ga alloys on NaCl using pulsed laser deposition and present a simple way to release the film from its substrate and to realize free-standing Ni-Mn-Ga structures.

Molecular-level dynamic simulations are performed to investigate the mechanisms of molecular ejection and transport in laser ablation of frozen polymer solutions, as related to the matrix-assisted laser evaporation (MAPLE) technique for polymer film deposition. Coarsegrained description of molecular matrix and polymer molecules is used in the model, allowing for large-scale simulations of the ejection of multiple polymer molecules from MAPLE targets with different polymer concentrations, from 1 to 6 wt.%. The ejection of polymer molecules is observed only above the threshold for the collective material ejection (ablation). Ablation is driven by the phase explosion of the overheated matrix material, which proceeds through the formation of a foamy transient structure of interconnected liquid regions that subsequently decomposes into a mixture of liquid droplets and gas-phase matrix molecules. The polymer molecules resist the decomposition of the transient foamy liquid structure and stabilize the matrix droplets. In all simulations the polymer molecules are ejected as parts of large matrixpolymer droplets/clusters that are likely to retain a large fraction of matrix material at the time of the deposition on a substrate. The ejection and transport of large matrix-polymer droplets is related to high-resolution scanning electron microscopy (SEM) images of polymer films deposited in MAPLE, where morphologies of the films are found to be indicative of active processes of matrix vaporization and escape from the deposited matrix-polymer droplets.

Considering the recent developments of the pulsed laser in the femtosecond domain, the possibility of conceiving a new laser assisted Tomographic Atom Probe has been nvisaged. The instrument is able to map out the 3D distributions of the atomic positions in a volume about 20×20×200 nm³. By combining a standard atom probe to a femtosecond laser, it is possible to obtain excellent atom probe performances. The mass resolving power of the instrument is increased by a factor 3. The feasibility of a laser assisted Tomographic Atom Probe is thus demonstrated in conductive and non conductive materials.

A state of the art Penning trap is being developed at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University to make precision mass measurements of rare isotopes. The system relies on thermalizing nuclear reaction products in a helium-filled cell and then extracting them from the gas through ion-manipulation and differential pumping. Atomic ions and clusters are needed to calibrate various aspects of the entire system such as transport efficiency and the main magnetic field. High-power laser ablation has proven to be a successful method for producing a wide range of ions under various conditions, including atmospheric pressure. We have developed a laser ablation system to explore the production of test beams using a variety of targets. Laser ablation studies of C, Al, Au, Ag, Cu, Fe, and Zn were carried out in a test chamber with the second harmonic, 532 nm, from a Q-switched Nd:YAG laser. Many studies were carried out under vacuum using an ion-drift system and mass analysis in a quadrupole mass filter. The ablation target and laser optics were moved to the gas cell used to collect the nuclear reaction products and several ablation studies were performed. An overview of the laser-ablation system as well as some of the results of this work will be presented.

The small size of most of the present-day films produced by PLD (up to few cm²) is not only a general limiting factor for applications in many scientific and technical fields, but is also problematic for studies of samples for which edge effects may play an important role. Yttria-stabilized zirconia (YSZ) films with a uniform thickness have been deposited at different distances from the target and at different oxygen background pressure in the largearea PLD facility at Risø National Laboratory. Films of uniform thickness up to 300 nm and 1200 nm over an area with a diameter of more than 90 mm were achieved. Depending on the oxygen background pressure the YSZ films were found to grow in a highly oriented manner on the Si wafer.

We report the first successful deposition of cinnamate-pullulan polysaccharide thin films by Matrix Assisted Pulsed Laser Evaporation (MAPLE). Thin film depositions were performed in vacuum using a KrF* excimer laser source (λ = 248 nm, τ ≈ 20 ns) operated at a repetition rate of 10 Hz. The dependence on incident laser fluence of the induced surface morphology is studied. We demonstrated by Raman spectroscopy that our MAPLE-deposited cinnamate-pullulan thin films are composed of starting materials preserving their chemical structures, with no impurities.

Effect of laser ablation on properties of remaining material was investigated in silicon. It was established that laser cutting of wafers in air induced doping of silicon by carbon. The effect was found to be more distinct by the use of higher laser power or UV radiation. Carbon ions created bonds with silicon in the depth of silicon. Formation of the silicon carbide type bonds was confirmed by SIMS, XPS and AES measurements. Modeling of the carbon diffusion was performed to clarify its depth profile in silicon. Photo-chemical reactions of such type changed the structure of material and could be a reason for the reduced quality of machining. A controlled atmosphere was applied to prevent carbonization of silicon during laser cutting.

Synthesis of high-purity single-walled carbon nanotubes (SWNTs) is demonstrated by a laser heating catalytic CVD method. This method makes it possible to produce SWNTs without the use of an electric furnace or hot filament. SWNTs were synthesized from alcohol using Fe/Co catalyst particles supported on zeolite and Mo/Co particles deposited directly on a substrate. Synthesis of high purity SWNTs was confirmed by in situ Raman scattering analysis and AFM and FE-SEM observations.

Controlling the absorption mechanism, e.g. inverse Bremsstrahlung and resonant absorption, the emission of Si-K_α-radiation using focused femtosecond laser radiation (t_p = 100fs, λ = 850 nm, I = 20 PW/cm²) has been investigated. The emission Si-K_α-radiation has been improved with double pulses, varying the delay, the energy ratio between pre- and main-pulse and the focal position. The efficiency for double-pulse-generation of Si-K_α-radiation has been increased 4 times compared to single pulse generation.

A combined mathematical and computational model is developed for simulation of physical processes accompanying the ablation of carbon particles in an aerosol under influences of short laser pulses. The model describes absorption of laser radiation by particle material, heating and evaporation of a particle, vapor expansion into an ambient gas and formation and growth of clusters. Heating of a particle is described by the heat conduction equation. Varying of the particle's shape is taken into account. Expansion of vapor and its mixing with ambient gas are modelled by the direct simulation Monte Carlo method. Modeling of nucleation and growth of carbon nanoclusters is performed with the help of a kinetic model based on the Smolukhovskiy's rate equation. The size of carbon particles, the fluence and the duration of laser pulse are varied in computations. The influence of the particle size on the mass of the evaporated material is studied. Cluster's size distributions are obtained and analyzed.

Laser swelling of borosilicate and soda-lime glass is shown for wavelengths of 193 and 248 nm. Very smooth patterns up to 45 nm high were generated by KrF laser (248 nm) irradiation of borosilicate glass at a fluence of 1.5 J/cm². At 193 nm laser wavelength, lower heights (up to 13 nm) and lower swelling threshold fluences (0.1 J/cm²) were observed due to higher material absorption. For the less absorbing soda-lime glass higher fluences than for the borosilicate glass are needed to establish elevated structures. Gratings in borosilicate glass with sub-micron periodicity demonstrate the high resolution of the method. The results can be explained by a thermo-physical model based on the change of the glass transition temperature due to fast cooling after the pulsed laser irradiation.

The etching of fused silica substrates by employing the process of laser-induced backside wet etching (LIBWE) using the laser radiation of a 248nm, 500fs excimer laser and a 775nm, 130fs Ti:sapphire is presented here for the first time. Etched volume results are presented in combination with topological investigations of the etched areas performed by SEM scans, revealing new aspects of the nature and products of the process.

Laser processing has found an important application in the hard disk drive (HDD) industry to fabricate bumps for screen testing of the manufactured magnetic disk media prior to HDD assembly. The flying height of the head slider needs to be calibrated by a specifically designed bump array. With areal density of HDD already exceeds 100Gbits/in², the head slider flies at 6 nm flying height and will become even lower. Sub-10nm bump height, as low as 3.5nm, is required to match future slider flying height. In this study, bump arrays with sub- 10nm bump height, good height uniformity and precise distribution was fabricated on glass disk substrate using an integrative control system consisting of a pulsed CO₂ laser and a high precision stage. The bump disk requirements were demonstrated successfully and compared with industrial specifications.

The hydrodynamics including the optical breakdown and shock wave formation is central to the analysis of the laser shock cleaning (LSC) process. In this work, a 2-dimensional theoretical model is proposed for computation of the hydrodynamic phenomena occurring in the LSC process. It is demonstrated that the results of the numerical computation are in good agreement with experimental observations and reveal the details of the physical mechanisms underlying the LSC process. Furthermore, the hydrodynamics of gas jet injection to sweep the detached particles away is investigated employing the theoretical model.

Laser ablation (LA) of a Ag target in ultrapure water has been performed with nanosecond laser pulses of 355, 532 and 1064 nm in the range of fluences achievable for the particular wavelength. Efficiency of LA process was quantified in terms of the amount of ablated Ag as determined by atomic absorption spectroscopy (AAS) as well as of the area of the surface plasmon extinction (SPE) band of the resulting Ag nanoparticle hydrosol, and a fairly good agreement between the results produced by the two methods was obtained. Sigmoidally shaped plots of the LA efficiency as a function of laser fluence were obtained for LA with all wavelengths of laser pulses examined. Nevertheless, the maximum amount of Ag transferred from the target into the aqueous medium (yielding Ag nanoparticle hydrosol) is substantially (at least 6.5 x) larger for LA performed with 1064 nm pulses than that with 532 nm and 355 nm pulses. On the other hand, polydispersity of the hydrosol ablated with 1064 nm pulses is higher than that of the sols obtained with 532 and 355 nm pulses, most probably due to a limited extent of Ag nanoparticle fragmentation.

A novel approach, based on reactive laser ablation in oxygen, is proposed to synthesize Si and Ge nanoparticles embedded in SiO₂ and GeO₂, respectively. We observe a significant photoluminescence (PL) that strongly depends on the oxygen pressure. The size of nanoparticles, estimated from PL spectra, decreases with increasing oxygen pressure. The maximum PL was observed at an oxygen pressure of 0.8 mTorr for Si and 10 mTorr for Ge, corresponding to a size of 2.2 nm and 1.9 nm, respectively. We discuss the similarities and the differences between the PL properties and formation mechanisms of the Si/SiO₂ and Ge/GeO₂ systems.

This work investigates the effect of polymer molecular weight M_W on the UV ablation of iodo-naphthalene- and iodo-phenanthrene-doped poly(methyl methacrylate) PMMA, and polystyrene PS films following irradiation at 248 nm. For irradiation at weakly absorbed wavelengths, the ablation threshold increases with increasing M_W. However, at strongly absorbed wavelengths, the difference in the ablation thresholds is much smaller, or minimal. In parallel, bubble formation due to accumulation of gas produced by polymer and dopant decomposition differs depending on M_W. For highly absorbing PS, the differences of behaviour show a less dramatic dependence on M_W. These results are explained within the framework of the bulk photothermal model, according to which ejection requires that a critical number of bonds is broken. In all, they are of direct importance for the optimisation of laser processing schemes and applications and provide the first indication of explosive boiling in UV ablation of polymers.

Laser ablation of Ag in water, and in N₂ gas atmosphere for comparison, has been studied by emission spectroscopy. A self-reversed dip in the emission line of Ag (I) appearing at around 338 nm was investigated. Shift of the wavelength of the self-reversed dip was observed. The shift was larger in water than in N₂ gas atmosphere. The relation between the density and self-reversed dip was investigated.

Promoting effect of citrate in 1 × 10⁻⁵−1×10⁻² M concentrations on laser ablation (LA) of a Ag foil in aqueous solution performed by ns laser pulses at 1064 nm is reported. Furthermore, adsorption of citrate ions was found to increase markedly the stability of the resulting LA-Ag hydrosol. The results are discussed on the basis of comparison of surface plasmon extinction spectral characteristics, transmission electron microscopy images, nanoparticle size distributions and surface-enhanced Raman scattering (SERS) spectral tests of hydrosols resulting from LA in neutral and acidic aqueous citrate solutions and in pure water.

Surface-relief gratings on optical materials are required for various telecommunication applications, as light couplers for planar optical waveguides, Bragg reflectors, or alignment grooves for liquid crystals. Vacuum-UV-laser ablation enables precise machining of fused silica. A comparison of ablation results obtained at 157 nm and 193 nm wavelength leads to the following conclusion: at 193 nm the surface properties (e.g. mainly roughness) have strong influence on the ablation behaviour. At 157 nm, the volume properties (e.g. mainly bulk absorption) are dominating instead. Though there are severe constraints concerning deep hole drilling at 193 nm, because irregular cracking can hardly be excluded, the generation of high resolution surface patterns is possible at this laser wavelength. As an example, sub-half-micron surface-relief gratings were fabricated on fused silica by laser ablation with nanosecond (ns) pulses at 193 nm from an ArF excimer laser. The grating relief was generated by imaging a transmission amplitude grating with a Schwarzschild objective of 25x demagnification. To provide high resolution in combination with high fluence, which is required for ablating fused silica, an off-axis mask projection scheme utilizing superposition of the zero order beam with the +1st diffraction order was applied.

This work has shown the existence, for the purpose of experiments of laser-induced plasma spectroscopy, of an apparent (population-averaged) excitation temperature that determines with good approximation the Boltzmann population distribution for each ionisation species. In experiments in which the line intensity (integrated along the line-of-sight) is measured, the values of the apparent temperature obtained for neutral atoms and ions are different. To investigate the population-averaging process, a plasma generated with a Ni-Fe-Al alloy in air at atmospheric pressure has been characterized with complete spatial resolution, determining the local values of the electronic temperature and the relative number densities of Fe neutral atoms and ions. From the distributions of plasma parameters, synthesized distributions of intensities integrated along the line of sight have been obtained for Fe I and Fe II lines, showing good agreement with the experimental distributions. Synthesized Boltzmann plots of neutral atoms and ions, constructed with the spatially-integrated synthesized intensities, have shown linear behaviors, providing the apparent temperatures for neutral atoms (9890 K) and ions (11400 K). The synthesized Boltmann plots are also in good agreement with experimental Boltzmann plots obtained in independent spatiallyintegrated measurements of the plasma emission, carried out with a fiber optics cable.

The preparation of the epitaxial Pb(Zr,Ti)O₃:PZT film on SrTiO₃: STO, LaAlO₃: LAO, MgO and La_0.7Sr_0.3MnO₃: LSMO / LAO substrates using the excimer laser-assisted metal organic deposition (ELAMOD) process was investigated. When using the STO substrate, the epitaxial PZT film was obtained by the ArF laser irradiation at room temperature using the 2-step irradiation method. On the other hand, when using the LAO and MgO substrates, no single phase of the PZT film was obtained by the ArF laser irradiation at room temperature. The LSMO buffer layer was prepared on the LAO substrate by thermal MOD at 1000°C, and the PZT film was then prepared on the LSMO / LAO substrate by ELAMOD at room temperature. The effects of the laser fluence, shot number and buffer layer thickness on the PZT epitaxial growth were investigated. An epitaxial PZT / LSMO / LAO film was successfully obtained by ArF laser irradiation at 80mJ/cm² and room temperature. The formation mechanisms of the epitaxial PZT films by ELAMOD are also discussed.

Epitaxial and polycrystalline SnO₂ thin films were prepared by the excimer laser annealing of amorphous SnO₂ films on TiO₂ (001) and MgO (001) substrates. The amorphous SnO₂ film was prepared by a metal organic deposition (MOD) using di-n-butylbis (2, 4-pentanedionate) tin at 300°C. The crystallinity and orientation of the product films were investigated by the XRDΘ—2Θ, pole figure and transmission electron microscopy (TEM) analyses. At 200 mJ/cm², the (002) oriented SnO₂ films were obtained by KrF laser irradiation. Using the XRD φ scanning measurement and TEM, it was found that the oriented SnO₂ films were epitaxially grown on the (001) TiO₂ substrate. On the other hand, the polycrystalline SnO₂ film was obtained on the MgO (001) substrate. It was found that the grain size of the SnO₂ film on the MgO substrate near the surface is larger than that of the near substrate based on crosssectional bright field TEM micrographs.

Optical emission spectroscopy of the pulsed laser ablation of spines and glochids from Opuntia (Nopal) cladodes was performed. Nopal cladodes were irradiated with Nd:YAG free-running laser pulses on their body, glochids and spines. Emission spectroscopy analyses in the 350-1000 nm region of the laser induced plasma were made. Plasma plume evolution characterization, theoretical calculations of plasma plume temperature and experiments varying the processing atmosphere showed that the process is dominated by a thermally activated combustion reaction which increases the dethorning process efficiency. Therefore, appropriate laser pulse energy for minimal damage of cladodes body and in the area beneath glochids and spines can be obtained.

Results related to the peculiarities of light scattering by nanoparticles and nanowires near plasmon resonance frequencies are reported. It is shown that the scattering problem for weakly dissipative media cannot be analyzed in the dipole approximation, in contrast to the classical Rayleigh scattering. A structure of the Poynting vector in the near field area is obtained. It is shown that small variations of the size parameter or/and the incident light frequency may lead to drastic transformations of the near field distribution.

In this paper we present a multi-step laser tailoring process in order to narrow the size distribution of self-assembled supported metal nanoparticles. The method exploits the shape and size dependent optical absorption coefficients of metal particles. Silver nanoparticles were prepared by deposition of atoms on dielectric substrates followed by diffusion and nucleation. This results in ensembles of oblate nanoparticles with broad size and shape distributions. Post-growth irradiation allows tailoring the average size of the nanoparticles by laser-induced surface diffusion and evaporation of surface atoms of the nanoparticles. This makes it possible to shrink large particles to the desired size and remove all nanoparticles that are too small. We demonstrate here that the size distribution of silver nanoparticles can be narrowed significantly by subsequently applying different laser wavelengths.

Precise and periodic structure can be formed on and inside materials by interfering femtosecond laser processing. In this method, laser ablation or modification is induced according to the interference pattern. In our technique, this method is applied to thin film processing, and nano-sized structures such as nanobumps, nanomeshs, and nanobelts. Nanobump array structure can be formed by periodic thermal processes induced by a single shot of interfering laser. Field emission from a nanobump array was demonstrated. By processing at relatively higher fluence, a grating, a circular or a ellipsoidal hole array structure can be generated according to the number of beams. By exfoliating the structures, nanobelt or nanomesh structure can be generated. This is a top-down technique for the generation of new nanomaterials.

We investigated the working mechanisms of femtosecond laser nanoprocessing in biomaterials with oscillator pulses of 80 MHz repetition rate and with amplified pulses of 1 kHz repetition rate. Plasma formation in water, the evolution of the temperature distribution, thermoelastic stress generation, and stress-induced cavitation bubble formation were numerically simulated for NA = 1.3 and the outcome compared to experimental results. A comparison of the thresholds for the various physical effects with experimental parameters enables to assess the working mechanisms of both modalities for cell surgery.

Core-shell nanoparticles composed of ferromagnetic cobalt platinum cores covered by non-magnetic silica shells were synthesized by laser ablating a composite target in a helium background gas. The average diameter of the CoPt core was controlled by adjusting the CoPt/SiO₂ ratio of the ablation target. The particles were also classified in the gas phase using an electrical mobility classifier. The present method successfully synthesized nearly monodispersed nanoparticles with an average core diameter of 2.5nm. This article describes the synthesis of the core-shell nanoparticles and investigates their magnetic properties.

ZnO nanoparticles were synthesized by means of femtosecond laser ablation of a ZnO target in different pure liquids such as deionized water and ethanol, and in solutions of doand octa-decanethiol. Samples produced in water at low laser fluence contained nanoparticles whose radius is less than the Bohr radius as revealed by photoluminescence measurements that illustrate explicitly the effect of quantum confinement directly linked to the presence of nanoparticles. In fact, particles of about 1 nm in diameter were identified by AFM and TEM observations, which also show the increase in ablated particle size when increasing the fluence. Processing in ethanol and at low fluence led to the formation of ZnO particles of a few nanometers in diameter. When ablating in thiol solutions, slow cluster-growth promotes the formation of facetted particles.

Materials processing by ultrafast lasers offers several distinct possibilities for micro/nano scale applications. This is due to the unique characteristics of the laser-matter interactions involved, when sub-picosecond pulses are employed. Prospects arising will be discussed in the context of surface and in bulk laser induced modifications. In particular, examples of diverse applications including the development and functionalization of laser engineered surfaces, the laser transfer of biomolecules and the functionalization of 3D structures constructed by three-photon stereolithography will be presented. Furthermore, the removal of molecular substrates by ultrafast laser ablation will be discussed with emphasis placed on assessing the photochemical changes induced in the remaining bulk material. The results indicate that in femtosecond laser processing of organic materials, besides the well acknowledged morphological advantages, a second fundamental factor responsible for its success pertains to the selective chemical effects. This is crucial for the laser cleaning of sensitive painted artworks.

In this work, we investigate light concentration in nanoscale ridge apertures and its applications in nanomanufacturing. Optical transmission of ridge apertures in a metal film is optimized by numerical design using the finite-difference time-domain (FDTD) method. We show that ridge apertures provide an optical transmission enhancement of several orders of magnitude higher than regularly shaped nanoscale apertures, and also confine the transmitted light to nanoscale dimensions. We fabricated these ridge apertures in metal film coated on quartz substrates by focused ion beam (FIB) milling. These apertures are characterized by nearfield scanning optical microscopy (NSOM). The ridge apertures are also used as a nanoscale light source for nanolithography. Holes with sub-100 nm dimensions are produced in the photoresist with visible and UV laser illuminations. The performance of the ridge apertures is compared with that of regular nanoscale apertures to demonstrate their advantages and promising potentials for many near-field optical applications.

We have investigated micromachining of a variety of materials by irradiation with laser plasma soft X-rays (LPSXs) at around 10 nm. The pulsed LPSXs were generated by irradiation of a Ta target in a vacuum chamber with Nd:YAG laser light at 532 nm, with a pulse duration of 7 ns, at a fluence of ∼10⁴ J/cm². The LPSXs were focused on the surfaces of samples using an ellipsoidal mirror that is designed so that LPSXs at around 10 nm are focused efficiently. We found that quartz glass plates are ablated by LPSX irradiation at a typical rate of 48 nm/shot. Furthermore, the ablated regions have smooth surfaces with a roughness less than 10 nm after 10 shots of LPSX irradiation. It is demonstrated that quartz glass is machined with a lateral resolution higher than 100 nm. In addition to quartz glass, the LPSX processing can be applied to micromachining of a variety of materials such as Pyrex, CaF₂, LiF, LiNbO₃, Si and silicone.

Nanofabrication, at lateral resolutions beyond the capability of conventional optical lithography techniques, is demonstrated here. Femtosecond laser was used in conjunction with Near-field Scanning Optical Microscopes (NSOMs) to nanostructure thin metal films. Also, the possibility of using these nanostructured metal films as masks to effectively transfer the pattern to the underlying substrate by wet etching process is shown. Two different optical nearfiled processing schemes were studied for near-field nanostructuring. In the first scheme, local field enhancement in the near-field of a scanning probe microscope (SPM) probe tip irradiated with femtosecond laser pulses was utilized (apertureless NSOM mode) and as a second approach, femtosecond laser beam was spatially confined by cantilevered NSOM fiber tip (apertured NOSM mode). The minimized heat- and shock-affected areas introduced during ultrafast laser based machining process, allows processing of even high conductivity thin metal films with minimized formation of any interfacial compounds between the metal films and the underlying substrate. Potential applications of this method may be in the fields of nanolithography, nanofluidics, nanoscale chemical and gas sensors, high-density data storage, nano-opto-electronics, as well as biotechnology related applications.

We report optical limiting properties of carbon nanoparticles, which were made in liquids by laser ablation of a bulk carbon target. The carbon nanoparticles were analyzed with micro-Raman spectroscopy, UV-Vis spectroscopy and Electron microscopy. Optical limiting responses towards 532-nm wavelength were measured with a 7-ns Nd:YAG laser. Nanoparticle size and laser pulse repetition rate effects on optical limiting behaviour were studied. A model was proposed to explain the physical origin of this nonlinear optical process. This work can provide useful information for designing carbon nanoparticle based optical limiters.

The ablation mechanism of SiO at the laser wavelength of 266 nm has been investigated by characterizing the composition and dynamics of neutral and charged particles produced in the ablation. The neutral and ionized composition of the plume and the dynamics of neutral SiO were investigated by time-of-flight mass spectrometry. The velocity distribution of neutral SiO molecules shows contributions of slow and fast components. The velocity distributions of charged species in the plume were investigated by a Langmuir probe technique, obtaining that the distributions shift towards higher velocities with increasing distance from the target surface. The fastest component of the velocity distribution of neutral SiO overlaps the slowest part of the velocity distribution of charged species. The average rotational energy of SiO molecules, estimated by LIF spectroscopy does not allow to draw clear conclusions about the participation of silicon oxide ion clusters as the precursors of fast SiO molecules in the plume.

This work was aimed at achieving an optimal deposition process by pulsed laser ablation (PLA) on large area substrates, using pure tungsten as target. The films were deposited at different: wavelengths (355/532/1064 nm), fluences (1.5, 5 and 10 J/cm²), oxygen pressures (100 and 200 mTorr), substrate temperatures (room temperature, 200, 300, and 400°C). The morpho-structural and compositional investigations have been carried out by profilometer, scanning electron microscopy, X-ray diffraction, Rutherford backscattering spectroscopy and Fourier transform infrared spectroscopy. The study has shown that optimal conditions for tungsten deposition on large area surfaces are at 355 nm/ 5 J/cm². Amorphous, orthorhombic and triclinic phases WO₃ films were obtained.

This work examines a laser particle fragmentation process to enhance the thermal conductivity of nanofluids. A Q-switched Nd:YAG laser is employed to change the size of the suspended ZnO nanoparticles in water. The influence of laser irradiation on the suspended particles is analyzed by transmission electron microscopy and absorption spectroscopy. The thermal conductivity of the nanofluid is measured by the transient hot-wire method. The results show that laser irradiation leads to partial fragmentation of some particles. However, the partial size reduction results in substantial enhancement of the thermal conductivity.

Pulsed laser deposition (PLD) has been used to obtain thin films of poly(methyl methacrylate) and polystyrene doped with fluorescent probes, amino aromatic compounds S5 and S6, that could be used to sense the presence of contaminating environmental agents. These dopants both in solution and inserted in polymeric films are sensitive to changes in pH, viscosity and polarity, increasing their fluorescence emission and/or modifying the position of their emission band. Films deposits on quartz substrates, obtained by irradiating targets with a Ti:Sapphire laser (800 nm, 120 fs pulse) were analyzed by optical and Environmental Scanning Electron Microscopy, Fluorescence Microscopy, Laser-Induced Fluorescence, Micro Raman Spectroscopy and Flow Injection Analysis-Mass Spectrometry. The transfer of the polymer and the probe to the substrate is observed to be strongly dependent on the optical absorption coefficient of the polymeric component of the target at the irradiation wavelength.

The patterning of sub-micron periodicity Bragg reflectors in Er/Yb-codoped IOG1, phosphate glass is demonstrated. A high yield patterning technique is presented, wherein high volume damage is induced into the glass matrix by exposure to intense UV radiation, and subsequently a chemical development in a strong acid selectively etches the exposed areas. The grating reflectors were fabricated by employing an elliptical Talbot interferometer and the output of a 213nm, 150ps frequency quintupled Nd:YAG laser. The grating depth of the etched relief pattern in time was measured at fixed time intervals and the dependence is presented in upon the etching time and exposure conditions. The gratings fabricated are examined by atomic and scanning electron microscopy for revealing the topology of the relief structure. Gratings with period of the order of 500nm were fabricated, having a maximum depth of 60nm.

The morphology of polymer films deposited with the matrix-assisted pulsed laser evaporation (MAPLE) technique is explored for various target compositions and laser fluences. Composite targets of 1 to 5 wt.% poly(methyl methacrylate), PMMA, dissolved in a volatile matrix material, toluene, were ablated using an excimer laser at fluences ranging from 0.045 J/cm² to 0.75 J/cm². Films were deposited on Si substrates at room temperature in a dynamic 100 mTorr Ar atmosphere. Scanning electron microscopy (SEM) imaging revealed that the morphology of the deposited films varied significantly with both laser fluence and PMMA concentration. The morphologies of large deposited particles were similar to that of deflated ''balloons''. It is speculated that during ablation of the frozen target, clusters comprised of both polymer and solvent ranging from 100 nm to 10 μm in size are ejected and deposited onto the substrate. The solvent begins to evaporate from the clusters during flight from the target, but does not completely evaporate until deposited on the room temperature substrate. The dynamics of the toluene evaporation may lead to the formation of the deflated structures. This explanation is supported by the observation of stable polymer-matrix droplets ejected in molecular dynamics simulations of MAPLE.

The stimulation of carbon nanotubes (CNT) growth in a thermal CVD process using an acetylene/nitrogen gas mixture by KrF-excimer laser exposure of iron nitrate coated silicon is described. At moderate laser fluences of ∼1 J/cm² the growth of nanotube bundles up to 100 μm consisting of vertical aligned multi-walled carbon nanotubes (VA-MWCNT) is observed. AFM measurements show the formation of nanoparticles in the laser-exposed areas. At this catalytic sites the nanotubes grow and sustain one another and forming the well-defined bundles. Via the laser exposure the control of the catalytic sites formation and consequently the nanotube growth and properties can be achieved.

The results from our recent molecular dynamics and electronic calculations studies of the interaction of ultraviolet light with poly(methyl methacrylate) are discussed. Molecular dynamics simulations in the photochemical and photothermal regimes demonstrate the delayed onset of ablation due to the slow pressure relaxation in the polymeric material. Electronic structure calculations show the possible wavelength-dependent pathways of exothermic and endothermic release of gaseous and small molecules which could induce the ablation pocess. The results from our studies are the centerpiece for the current development of the mesoscale model of the light irradiation of polymeric material.

An ongoing study of the scaling of Laser-Induced Breakdown Spectroscopy (LIBS) to microjoule pulse energies is being conducted to quantify the LIBS process. The use of microplasmas for LIBS requires good understanding of the emission scaling in order to maximize the sensitivity of the LIBS technique at low energies. The quantitative scaling of emission of Al, Cu and Si microplasmas from 100 μJ down to 100 nJ is presented. The scaling of line emission from major and minor constituents in Al 5052 alloy is investigated and evaluated for analytical LIBS. Ablated crater volume scaling and emission efficiency for Si microplasmas are investigated.

Sub-wavelength ripples (<λ/4) are obtained by scanning a tightly focused beam (∼1μm) of femtosecond laser radiation (t_p = 100fs, λ = 800nm & 400nm) over the surface of various materials. The ripple pattern extends coherently over many overlapping laser pulses parallel and perpendicular to the polarisation. Investigated are the dependence of the ripple spacing Δ on the material. New results concerning the dependence of the spacing on the wavelength are presented. Some possible models for ripple growth are discussed and conditions under which these phenomena occur are contained. In opposition to the classical ripple theory, the observed ripple spacing is dependent on the material, giving indication to understand the processes during the sub-wavelength ripple formation by femtosecond laser radiation.

Time resolved shadowgraph images were recorded of shockwaves and particle ejection from silicon during laser ablation. Particle ejection and expansion were correlated to an internal shockwave resonating between the shockwave front and the target surface. The number of particles ablated increased with laser energy and was related to the crater volume.

To study the expansion and cooling process of the laser induced plasma generated by nanosecond pulsed laser ablation, experiments have been conducted which measure the position of the external shockwaves and the temperature of the vapor plumes. The positions of external shockwaves were determined by a femtosecond laser time-resolved imaging system. Vapor plume temperature was determined from spectroscopic measurements of the plasma emission lines. A model which considers the mass, momentum, and energy conservation of the region affected by the laser energy was developed. It shows good agreement to the experimental data.

Carbon nanofibers (CNFs) were grown on metal-catalyzed Si substrates by pulsed laser ablation of graphite. Metal catalysts, Ni, NiCo, Pd and PdNi, were respectively deposited on Si substrates with a SiO₂ layer of 200-nm thickness by a dip coat method, and the substrates placed in a laser oven apparatus. By pulsed laser ablation of graphite for 2 hours, CNFs were grown at oven temperatures ≥ 1000°C. Diameters of grown CNFs were about 20-30 nm by scanning electron microscopy, and increased with oven temperature. The difference of CNF growth by the catalysts was shown. Pd-contained catalysts grew thicker CNFs than the other catalysts; while PdNi and NiCo yielded a higher number density of CNFs than the other catalysts. CNF diameter and length changed according to the substrate position from the target. We also discussed the growth mechanism of CNFs with this method.

We review results of the femtosecond laser ablation of noble metals in pure water to synthesize colloidal nanoparticles. We show that such ablation leads to the formation of two different populations of nanoparticles (low and highly size-dispersed ones), while their mean size and relative contribution are strongly affected by the intensity of pumping radiation. Analyses of ablation craters on the target surface enables to relate the appearance of these populations to photon- and plasma-induced ablation mechanisms, respectively. The nanoparticles produced are of importance for biological sensing and imaging applications.

Femtosecond laser ablation of organic molecules has been investigated to develop an elemental analysis technique for these samples. Behaviour of Sm⁺ emitted from organic molecules settled on chosen substrates was studied by the two-dimensional laser induced fluorescence method. Comparisons among substrates of a quartz glass, Si and Ta are presented with the parameters of a kinetic energy and a spreading velocity of Sm⁺. The kinetic energy of Sm⁺ emitted from the sample on the quartz glass was the highest and decreased for the Si and Ta. Moreover, it is found that the spatial distribution of Sm⁺ on the Si substrate tends to barely spread in the transverse direction. We observed that the ablation dynamics of the organic molecules on the substrate are affected by the substrate material.

We report that the kinetic energy of samarium (Sm) atom and Sm⁺ ion produced by femtosecond laser ablation of solid samarium is strongly dependent on the number of ablation laser shots in the range from 1 to 10. By ablating the fresh surface (i.e. 1st shot), we find the kinetic energy of both Sm and Sm⁺ ion to be the largest (24 and 250 eV, respectively). Almost 10 times larger kinetic energy of Sm⁺ ion than that of Sm clearly indicates the contribution of Coulomb explosion in the acceleration process. From the second shot, kinetic energies of Sm and Sm⁺ ion are lower than those of the first shot and almost constant (ca. 12 and 80 eV, respectively). This behaviour suggests the change in the nature of the solid surface after femtosecond laser ablation, which can be explained by the amorphization of ablated sample surface reported in recent studies.

Low frictional, textured diamond-like carbon (DLC) films were deposited onto silicone [SiO(CH₃)₂]n] rubber by femtosecond laser ablation of frozen pentanel (C₅H₁₁OH). Deposition rate of the films for silicone rubber was higher than that for Si wafer. A broad Raman peak centred at 1530 cm⁻¹ was measured from the films deposited on silicone, showing a DLC film. The Raman spectra of the DLC films on silicone and Si wafer, a textured DLC films were also formed on silicone rubber. A coarse texture of the films was obtained by increasing the deposition time. The textured DLC films could improve frictional property of a sticky silicone rubber.

We have compared time-of-flight mass spectra for an inorganic and a biological macromolecular sample applied on a silicon substrate obtained by laser ablation with femtosecond and nanosecond lasers. Many fragment peaks appeared in the mass spectra for nanosecond laser ablation. In contrast, the samples were effectively atomized to monoatomic ions by femtosecond laser ablation. We find that femtosecond laser ablation has a great advantage in an elemental analysis of solution samples on a substrate. Silicon clusters Si_n (up to n = 6) from the substrate were also observed.

We prepare high quality thin films of β-FeSi₂ on silicon substrates by an ArF excimer laser deposition method (ArF-PLD) using -FeSi alloy targets. Preferentially [100]- oriented β-FeSi₂ films were grown on Si(100) surfaces, and the interface between the films and substrates are very smooth. Based on a fact that when iron silicide films are obtained on sapphire substrates in stead of the silicon ones, the films have the same compositions as the target materials, silicon atoms in the β-FeSi₂ films must be supplied from the silicon substrates.

By using laser-induced backside wet etching (LIBWE), we have fabricated very deep micro-trenches in silica glass of 9-μm width and 300-μm depth (aspect ratio ≈ 33). In this paper, we present the details of fabricating the micro-trenches, and discuss why such a deep micro-trench is available by the LIBWE method.

The average kinetic energy of Zn⁺ ions and optical emission intensities from Zn* and Zn^+* produced by laser ablation of a Zn target were measured as a function of bias voltage applied to a grid mounted facing the target to elucidate the effects of the external electric field on the laser-produced plasma plume. It turned out that the relative concentration of the ionic species in the plume increased and the crystallinity of the deposited ZnO film improved with increasing the bias voltage.

Cubic ZnS semiconductor nanocrystals with the size of 2 to 5 nm were prepared by pulsed laser ablation in aqueous surfactant solutions of sodium dodecyl sulfate and cetyltrimethylammonium bromide without any further treatments. The obtained suspensions of the nanocrystals have broad photoluminescence emission from 375 to 600 nm. The abundance and emission intensity of the nanocrystals depend on the concentration of the surfactant in solution.

We performed pulsed laser ablation (PLA) of a silicon target in liquid environment to prepare a silicon colloid solution. The nanoparticles were observed by SEM and TEM measurements. The result of Raman scattering indicates that this particle is mainly composed of silicon nanocrystallites. The optical gap energies of the colloid solutions varied by changing the solvents; 2.9 and 3.5 eV for colloids prepared in water and hexane, respectively. These colloid solutions showed efficient PL intensity. Since Si-(CH₃)_n related bonds were observed for the specimen prepared in hexane, surface effects other than the quantum confinement effect should be taken into account for the origin of the PL. Our results indicate that new kinds of Sibased colloid solutions can be prepared by PLA in solvent. Since the PL peak energies were sensitive to the surface conditions, these colloid solutions are promising for biological applications such as bio-sensors.

Dot-array patterns with a-few-µm period were formed on oxidized-Si substrates by Fresnel diffraction of Ti:sapphire femtosecond laser radiation. Si wafers were coated with thin SiO₂ films in order to prevent the surface degradation during laser processing. SiO₂ layers with various thicknesses from 0 to 1.2 µm were grown by thermal oxidation, and exposed to several laser conditions. The modified surface morphology and the depth of the dots were characterized, revealing periodic fine patterns of 3-µm depth for 0.2-µm SiO₂/Si samples irradiated for 30 s at 130-mJ/cm² laser fluence.

The decomposition of Gd₃Ga₅O₁₂ single crystal target induced by a KrF excimer laser pulse during the deposition process was observed. This phenomenon was studied ex situ by EDX analyse of ablated target and in situ by Optical Emission Spectroscopy of the laser plasma. The decomposition process depends mainly on the absorption coefficient of the target on the corresponding laser wavelength and oxygen partial pressure in the deposition chamber during laser ablation. Taking into account the differences between absorption coefficients of Pr:Gd₃Ga₅O₁₂ and Yb:Gd₃Ga₅O₁₂ targets the Pr:GdGaO₃ and Yb:GdGaO₃ thin films were successfully fabricated at different oxygen pressures of 1 Pa and 2.5 Pa, respectively. The structural properties of the fabricated films were studied by RBS and XRD.

The possibilities to grow isolated structures of complex oxides by pulsed laser deposition through stencils were investigated. A stencil consisting of a SiN membrane with apertures of several hundred nanometers embedded in a Si chip is placed in front of a heated substrate (up to 750 degrees Celsius). Deposition through these apertures results in resistless, direct patterning by local deposition of complex oxides like ferroelectric Lead Zirconate Titanate. The created isolated structures were analyzed by AFM imaging. Under-deposition, in this work called broadening, is inevitable during stencil deposition and is depending on deposition parameters, especially pressure. Different causes of broadening are mapped and discussed.

This paper presents a flexible, mask-free and efficient technique for UV-laser micropatterning of photosensitive resist by laser direct writing (LDW). Photo resist spun on gold sputtered silicon wafers has been laser structured by a scanner guided 266nm DPSSL and electroplated. Ablation behaviour and optimum seed layer preparation in relation to parameters like pulse energy, scanning speed and number of scanned cycles and the electroplating results are discussed. The resulting adhesive strength was measured by a µ-sear device and the gold seed layer-plated copper interface investigated by SEM and EDX to explain correlation to identified bonding behaviour. Improved adhesive strength was observed with higher laser pulse energy and reduced number of cycle.

Short pulse laser melting and resolidification of a metal target are investigated in continuum and atomistic computer simulations. The cooling rates achievable in laser quenching are calculated within the framework of two-temperature model for a range of laser fluences and pulse durations. A well-defined maximum in the cooling rate dependence on the pulse duration and fluence is observed and explained by the competition between the electronic heat conduction and the energy transfer from the electrons to the lattice due to the electronphonon coupling. The results of molecular dynamics simulations demonstrate that the short pulse laser melting and recrystallization take place under highly non-equilibrium conditions that have a strong effect on the time-scales, rates, and other parameters of all the involved processes. An emission of partial dislocations from the melting front and their retreat at later times is observed in the simulations.

Thermal energy remaining in Sn and Ti samples following femtosecond and nanosecond laser ablation is studied as a function of laser fluence and ambient gas pressure. When the laser fluence is above a certain threshold value, we find a significant enhancement in residual thermal energy deposition in air but a decrease in vacuum, and these effects occur for both femtosecond and nanosecond laser ablation. In contrast to the previous belief, our study demonstrates that femtosecond and nanosecond laser ablation share similar residual thermal effects.

We report on the deposition of carbon nanotubes and nano-onions at room temperature using excimer laser radiation at 248 nm to ablate mixed graphite-nickel/cobalt targets in the presence of O₂ gas. The carbon nanotubes are frequently seen to connect individual onions and have a wall thickness on the order of 20-25 nm, with an overall external tube diameter of 100-200 nm. These tubes have notably large channel diameters and are significantly larger than typically reported single and multi-walled carbon nanotubes. The observed onion structures are both single and clustered and are 100-200 nm in diameter. Ablation of the same targets in comparable pressures of Ar does not result in these nanostructures but instead produces amorphous carbon. Ablating a pure graphite target under the same laser conditions, with or without metal, also does not yield the tubes and onions. In-situ time-resolved emission spectroscopy has been used to follow the emission from molecular carbon such as C₂, as well as metals such as Ni or Co in the different ambients.

Self-assembled monolayer (SAM) patterning on gold thin films was performed using 800 nm, 118 fs laser pulses. SAM removal was ablative and was observed at fluences near the multishot ablation threshold for the thin gold film. Line widths six times smaller than the 2 e-folding intensity beam diameter were observed demonstrating sub-diffraction limited patterning with femtosecond lasers. Similar experimental results in air and N₂ indicated that the removal process does not involve oxidation of the gold-sulfur bond as was claimed in the literature.

We have proposed a novel method which permits to grow silicon dioxide (SiO₂) films on various substrates at room temperature using silicone rubber. In the method, two F₂ laser (157 nm) beams are used. One is used for generation of source gases from the silicone rubber (1st laser). Another is used for illumination of a substrate to deposit the films (2nd laser). We study on characteristics of the deposited films using laser beams which have longer wavelengths than the F₂ laser beam. When a fourth harmonics of Nd:YAG laser (266 nm) is used as the 1st laser, SiO₂ films with no carbon contaminants are grown as same as the case that an F₂ laser is used. The films are consisted of granular structures and the grain size become small as the laser fluence of 2nd laser beam increase. When an ArF laser (193 nm) is used as the 2nd laser, the deposition rate of the films is very low and the films have carbon contaminants. It shows that the 2nd laser beam plays an important role not only in the growth of the films but also in the prevention of carbon contaminants being mixed into the film.

In this work we present evidence of photo-induced effects on crystalline Tungsten (W) films. A frequency doubled Nd:YAG (5ns) laser was used in our experiments. The W thin films were deposited on silicon substrates by the DC-sputtering technique using W (Lesker, 99.95% purity) targets in an argon atmosphere. The crystalline phase of the deposited W films was determined by X-ray diffraction. Our experimental results show clear evidence that several events take place as a consequence of exposure of the W films to the laser nanosecond pulses. One of those events has a chemical effect that results in a significant degree of oxidation of the film; a second event affects the structural nature of the initial W material, resulting into a material phase change; and a third event changes the initially homogeneous morphology of the film into an unexpected porous material film. As it has been confirmed by the experiments, all of these effects are laser fluence dependent. A full post exposure analysis of the W thin films included Energy Dispersive Spectrometry to determine the degree of oxidation of the W film; a micro-Raman system was used to explore and to study the transition of the crystalline W to the amorphous-crystalline WO₃ phase; further analysis with Scanning Electron Microscopy showed a definite laser-induced porosity which changes the initial homogeneous film into a highly porous film with small features in the range from 100 to 300 nm.

Laser ablation with pulse bursts was studied to increase the ablation rate of steel. Pulse bursts consisting of different numbers of pulses between one and three were used. The microablation with pulses from a multi-pulse Nd:YAG laser with a pulse duration between 20 ns and 60 ns, interpulse separations in the range of 0.1 to 80 μs and burst energies of up to 2 mJ was studied. The process was characterized in terms of ablation rate, ablation geometry, dynamic of plasma expansion and plasma parameters.

In the present article, we describe the process of nanoparticle formation during pulsed laser ablation in an inert gas atmosphere. We investigated the interaction between laser ablated plumes and shock waves using one dimensional Eulerian fluid dynamics equations combined with a rate equation relating to a classical nucleation model of supersaturated vapors. The initial values for the plume immediately after laser irradiation onto a silicon target were calculated based on stochastic thermodynamics, which was first used by Houle et al. We found a certain case wherein the rate of nanoparticle formation becomes higher when a reflected shock wave passes through the plume. In that particular case, mono-dispersed nanoparticles can be generated by carrying out nucleation and nanoparticle growth as separate processes.

Based on the combination of short pulse duration with short wavelength, UV ultrafast lasers provide unprecedented material processing quality. A high power UV ultrafast laser system comprises a Ti:sapphire front-end laser whose frequency tripled pulses are amplified in a UV excimer gain module. In this way, subpicosecond pulses are obtained at 248 nm with an average power of up to 10 W. Such pulses are ideally suited for the treatment of solid surfaces with sub-micron precision. A combination of diffractive optical masks with conventional imaging systems allows the generation of complex 2D structures with typical feature sizes of ∼ 200 nm on all materials including metals, semiconductors and dielectrics. A new technique for the fabrication of the phase masks or diffractive phase elements used in the experiments is based on excimer laser patterning of dielectric layers. Such phase masks feature a large processed area, high efficiency for VUV to NIR radiation and can be customized e.g. for perfect zero order suppression.

Various measures to reduce the incorporation of particulates (droplets) into boron nitride films prepared by pulsed laser deposition were investigated. These measures include the use of magnetic fields aimed at the separation of the ionized atomic species and the particulates on their way from the target to the substrate and the use of a second laser beam aimed at the destruction of the particulates by evaporation.

We present a theoretical study and experimental results on the formation of conical nano-tips on silicon thin films as a result of single-pulse excimer laser irradiation. The fabricated structures have heights of about 1 µm and apical radii of curvature of several tens of nanometers. An individual cone is formed when a mono-crystalline silicon film on an insulator substrate is irradiated in air environment with a single 25ns pulse from a KrF excimer laser, homogenized and shaped to a circular spot with diameter of several micrometers. Atomic force microscopy was used to study these structures. A simplified analytical model for the formation of these structures is proposed. We also present computer simulations of heat transfer in Si films that results from irradiation with a single laser pulse, shaped to a circular spot.

This paper focuses on the fabrication and characterization of crystalline Yb-doped sesquioxide films (Yb₂O₃, Yb:Lu₂O₃, Yb:Sc₂O₃) grown by pulsed laser deposition on single crystal sapphire (α-Al₂O₃) and quartz (α-SiO₂) substrates as well as on lutetia (Lu₂O₃) and scandia (Sc₂O₃) substrates. Such ytterbium doped active films can be promising for use in a thin-disk laser setup. X-Ray diffraction measurements show that the films grow highly textured along <111> direction. The ω-scan (rocking curve) shows deviation of the crystallite orientation ∼4° in case of Lu₂O₃ and Yb₂O₃ films and <1° for Sc₂O₃ films. Yb₂O₃ films reveal no luminescence at room temperature and the well known Yb³⁺ emission in the 975-980 nm region (zero-phonon line) can only be observed at temperatures below 20 K. A similar effect is observed in a bulk Yb₂O₃ crystal. Ytterbium emission and excitation spectra measured at room temperature for Yb(5%):Lu₂O₃ and Yb(4%):Sc₂O₃ films resemble those of the bulk crystal very closely. Luminescence decay lifetimes are also comparable to those measured in a bulk crystal. This indicates a high quantum efficiency of the Yb³⁺-emission and allows application of such films as active media for thin disk lasers.

We have investigated the fabrication of two types of Er-doped silicon oxide films. The films were prepared by ablating a Si target covered with a thin Er metal layer, by Nd:YAG laser light at 50 mJ/pulse in 40 Torr O₂ gas. After depositing the Er-dispersed SiO_x (x ∼ 1.4) films, the films were annealed in Ar gas. We found that Er-doped films deposited at (a) 4 J/cm² and (b) 100 J/cm² have the optimum annealing temperatures of 600°C and 900°C, respectively. Furthermore, we found that Er-doped films deposited at 4 J/cm² exhibit much more intense light emission at 1.5 µm than those deposited at 100 J/cm². For the Er-doped films deposited at 100 J/cm², it is evident that electron-hole pairs are generated in Si nanocrystallites precipitated in a SiO₂ film and that recombination energy is transfered to Er³⁺ ions that emit 1.5 µm light, via the lowest luminescent state in Si nanocrystallites.

For laser ablation plumes which are significantly ionised, Langmuir probes have proved to be a relatively simple and inexpensive tool for measuring the plume shape, ion energy distribution and electron temperature. In this paper we describe some recent work on the development of Langmuir probes for laser ablation plume diagnosis. Typically in laser ablation plasma the flow velocity is supersonic, which complicates the interpretation of the I-V probe characteristic. We describe some new work on the behaviour of a flat probe lying parallel to the plasma flow. We also compare our measurements with theoretical models of laser ablation plume expansion and draw some conclusions as to which model is more appropriate for the low temperature plasmas which arise in pulsed laser deposition.

Thin films of Er³⁺-doped tungsten tellurite glass have been prepared by the pulsed laser deposition technique using an ArF excimer laser. The depositions were performed at different O₂ pressure (5, 10 Pa) and at different substrate temperatures (RT, 100°C and 200°C). The composition and the optical properties of the deposited films, such as transmission, dispersion curves of refraction index and extinction coefficient, and film thickness were studied for the different deposition parameters. Transparent films at the highest substrate temperature were obtained only for a higher oxygen pressure with respect to the RT conditions.

Transition-Metal-doped TiO₂ thin films, with nominal composition Ti_0.9TM_0.1O_2-δ (TM = Mn, Fe, Co, Ni, Cu), were grown by pulsed laser deposition (PLD), in order to study the role of dopants in the origin and significance of room temperature ferromagnetism in these systems. The crystallographic structures and their magnetic properties were characterized and the experimental results are compared to ab-initio calculations previously reported. The films are ferromagnetic at room temperature in the cases of Fe, Co, Ni and even Cu impurities, but not in the case of Mn doping. Our results support the hypothesis that oxygen vacancies play a key role in the origin of magnetism in doped TiO₂ films, and can explain the diversity of magnetic moments observed experimentally for films grown under different conditions.

In this work, we investigate the polarity-dependent Electric Pulses Induced Resistive (EPIR) switching phenomenon in thin films driven by electric pulses. Thin films of _0.5Ca_0.5MnO₃ (manganite) were deposited by PLD on Si substrate. The transport properties at the interface between the film and metallic electrode are characterized in order to study the resistance switching. Sample thermal treatment and electrical field history are important to be considered for get reproducible EPIR effect. Carriers trapping at the interfaces are considered as a possible explanation of our results.

Femtosecond laser ablation of carbon nanotube (CNT) cathode was demonstrated in the laser fluence range of 0.05-2 J/cm². It was shown that the CNT ablated by femtosecond laser were aligned perpendicular to the cathode surface. The emission characteristics of the CNT cathode were measured using a diode system. The modified CNT cathode had a turn-on field of 1.8 V/μm, which was approximately half that of the original CNT cathode. As the laser fluence decreased, the turn-on field also decreased.

The properties of amorphous carbon nitride thin films, such as the composition, density, optical band gap, microstructure (sp³/sp² ratio), have been investigated as a function of the working gas pressure and the laser fluence used for deposition by pulsed laser ablation. The compositional characterization showed the presence of carbon, nitrogen, oxygen and hydrogen in the deposited films; the nitrogen content increased as the fluence increased reaching a maximum saturation value of 30.0 at. % at a nitrogen pressure of 7.5 × 10⁻² Torr. A similar behavior was observed when the fluence was kept constant and the gas working pressure was varied. The study of the optical properties showed that the optical band gap increased as the pressure and fluence were increased. The density of the deposits diminished as the nitrogen content increased suggesting the formation of a more porous material at higher N contents. The Raman results revealed that the I_D/I_G ratio increased monotonically with the increase of nitrogen content in the films indicating a rise in either the number or the size of the sp² clusters.

Normalized power transmitted functions obtained from the moving knife-edge method are used to determine the mode indices m and n of a TEM_m,n stigmatic Hermite Gaussian beam. It is shown that in a cross section plane, positions of zero laser beam irradiance coincide with points of zero slopes at corresponding curves of normalized transmitted power against positions of the knife-edge. The results hold for laser beams with a unique transversal electromagnetic mode. In addition, a criterion to estimate the half-width of high order Hermite Gaussian beams is proposed. Numerical calculations and graphic representations are carried out using MAPLE mathematical software.

We have studied water ice as a matrix for the production of PEG (polyethylene glycol) films by MAPLE at 355 nm. The deposition rate is small compared with other matrices typically used in MAPLE, but the deposition of photofragments from the matrix can be avoided. At temperatures above −50°C of the target holder the deposition rate increases strongly, but the evaporation pressure in the MAPLE chamber also increases drastically.

ZnO epitaxial thin films were grown on r-plane sapphire substrates, in a pulsed laser deposition apparatus assisted by an electron cyclotron resonance (ECR) N₂ plasma source. The resistivities and carrier concentrations (either n- or p-type) of the thin films were measured in a Hall effect apparatus as a function of the ECR source input microwave power and the substrate temperature, respectively. P-type conduction was observed in thin films grown in conditions of enhanced activation of the nitrogen ionic species. These experimental results are in qualitative agreement with recent theoretical calculations of the activation energies of the main donor defects compensating for N acceptors in ZnO.

We describe the stimulated emission and the field emission characteristics of ZnO nano-rod crystals synthesized by laser ablation in a background gas. A various type of nanostructured ZnO crystals were successfully synthesized on sapphire substrates, and ZnO crystals were taken out of the substrate by a laser brow-off technique and sonification. ZnO crystals taken out of the substrate showed a lower stimulated emission threshold than those as grown on the substrate under optical excitation, indicating a high quality of the crystalinity.

The pulsed laser ablation and deposition (PLD) processes of SrTiO₃ were studied as a model system for developing a technique for the growth of structurally bulk-equivalent epitaxial thin films of typical complex oxides. Deposition rate vs. laser fluence measurements showed that there is a second critical fluence value above the ablation threshold. Below the critical value, both the ablation and deposition rates are linear functions of the fluence and independent of the ablation spot area. Above the critical value, the deposition rate per unit ablation area depends strongly on the ablation spot area. Homoepitaxial SrTiO₃ films possessed the exact bulk lattice constant value only when the films were grown at the critical fluence, whereas larger lattice constants were obtained if the fluence was either higher or lower. Composition analysis revealed that the enlargement of the lattice constant was related to cationic unbalance. This critical laser fluence is essential for the growth of bulk-equivalent epitaxial films, and therefore accurate measurement of laser energy and ablation area is vital for reproducible film growth.

We developed a continuous-wave infrared laser molecular beam epitaxy (CW-IR-LMBE) optimized for the fabrication of organic semiconductor films. The crystal quality of these organic thin films deposited by CW-IR-LMBE was substantially the same as those deposited by thermal evaporation. Due to the possibility of quick switching of evaporation sources, CW-IR-LMBE is especially advantageous for rapid screening of composition, thickness, and fabrication parameters in materials and device optimization based on combinatorial technology.

A novel method for the fabrication of complex 3 dimensional structures, such as plano-convex microlens arrays in quartz, is presented. This technique is applied for precise micromachining of UV transparent materials, e.g. quartz, by using a conventional XeCl excimer laser and an organic solution which is in contact with the substrate. Strong absorption of the intense laser light results in the formation of the high pressure and temperature jumps at the quartz-liquid interface, which are the key elements in this process. A combination of laser assisted wet etching with the projection of a Diffractive Gray Tone Phase Mask is applied to fabricate diffractive and refractive micro-lens arrays in quartz. A quartz micro-lens array, which consists of 10 × 10 plano-convex microlenses is tested as a beam homogenizer for the quadrupled Nd:YAG laser.

We developed a novel technique fabricating 3D hollow microstructures embedded in photosensitive glass. The fabrication procedure consists of the following three steps: (1) femtosecond laser direct writing, (2) thermal treatment, and (3) wet etching in a diluted HF solution. The developed technique can fabricate various microcomponents such as microfluidics, microvalve, micromirror, microsplitter, freestanding fibre, and microfluidic laser. In this paper, integration of these microcomponents in a single glass chip by a single procedure is demonstrated for ''all-in-one'' lab-on-a-chip device manufacture.

Surface micro-structuring of silica glass plates was performed by using laser- induced backside wet etching (LIBWE) upon irradiation with a single-mode laser beam from a diode-pumped solid-state (DPSS) UV laser with 40 kHz repetition rate at 266 nm. We have succeeded in a well-defined micro-pattern formation without debris and microcrack generation around the etched area on the basis of a galvanometer scanning system for the laser beam. Bubble dynamics after liquid ablation was monitored by impulse pressure detection with a fast- response piezoelectric pressure gauge.

A single KrF laser pulse of energy larger than 0.5 J/cm² is enough to create a microfoam layer on the surface of a collagen film and other related biopolymers. This is a new result that can be of interest for many new applications. The target material is excited in the radiation absorption depth of ∼17 µm and expands into a foam layer whose new surface is ∼5 µm above the original one. The estimated surface transient temperature of ∼83°C at threshold fluence does not account satisfactorily for this fast foaming process but consideration of the bipolar pressure variation ∼±200 bar, i.e. laser induced acoustic wave suggests that a cold homogeneous boiling is induced by the tensile part of the pressure wave in the laser excited volume. The classical nucleation theory predicts a spontaneous dense and homogeneous bubble formation when the pressure is negative in the inviscid liquid. These results constitute new examples of laser induced fast expulsion of liquid due to the hydrodynamic pressure wave which can also be considered as resulting from the surface acceleration/deceleration sequence.

Due to their optical properties and morphology, thin films formed of nanoparticles are potentially new platforms for soft laser desorption/ionization (SLDI) mass spectrometry. Thin films of gold nanoparticles (with 12±1 nm particle size) were prepared by evaporation-driven vertical colloidal deposition and used to analyze a series of directly deposited polypeptide samples. In this new SLDI method, the required laser fluence for ion detection was equal or less than what was needed for matrix-assisted laser desorption/ionization (MALDI) but the resulting spectra were free of matrix interferences. A silicon microcolumn array-based substrate (a.k.a. black silicon) was developed as a new matrix-free laser desorption ionization surface. When low-resistivity silicon wafers were processed with a 22 ps pulse length 3×ω Nd:YAG laser in air, SF₆ or water environment, regularly arranged conical spikes emerged. The radii of the spike tips varied with the processing environment, ranging from approximately 500 nm in water, to ∼2 µm in SF₆ gas and to ∼5 µm in air. Peptide mass spectra directly induced by a nitrogen laser showed the formation of protonated ions of angiotensin I and II, substance P, bradykinin fragment 1-7, synthetic peptide, pro14-arg, and insulin from the processed silicon surfaces but not from the unprocessed areas. Threshold fluences for desorption/ionization were similar to those used in MALDI. Although compared to silicon nanowires the threshold laser pulse energy for ionization is significantly (∼10×) higher, the ease of production and robustness of microcolumn arrays offer complementary benefits.

We have studied the behavior of atoms and ions out of sample on a substrate ablated by femtosecond laser with one-dimensional (1D) and two-dimensional (2D) laser induced fluorescence (LIF) measurement. The sample of samarium standard solution spread and solidified on a Si (111) substrate was ablated by a femtosecond laser. Approximately half of the atomized samarium particles appeared to be neutral atoms and the other half did singly charged ions. It is found that the ablated Sm atoms and Sm⁺ ions have rather strong orientation to the surface normal, and the kinetic energy of Sm⁺ ions is larger than that of Sm atoms. Moreover, the kinetic energies of ablated Sm and Sm⁺ particles are similar to those obtained for the first-shot ablation of Sm solid sample, and are much larger than those of Sm and Sm⁺ after multi-shots.

The emission intensity of Ag(I) lines obtained by the laser ablation of an Ag plate immersed in water was examined. Due to an intense self-absorption in the plume, the spectral intensity of the emission approaches the Planck distribution, which is a function of temperature, but not a function of the population of the levels involved in the transition. The temperature obtained by assuming the Planck intensity agrees well with the previous study on the plume temperature in water. The result that the emission suffers from the intense self-absorption is a disadvantage for the use of emission spectra from the laser ablation plume in liquid as a quantitative elemental analysis of solid surfaces in liquid.

We adopted spectroscopic diagnostics for investigating plasmas produced by laser ablation of a graphite target in water. By taking pictures of optical emissions at various delay times after the irradiation of the ablation laser pulse, we examined the size, the lifetime, and the transient expansion of the plasma. The spectrum of the optical emission was also measured at various delay times. No line emissions were observed in the spectrum. The blackbody temperature of the plasma was evaluated by fitting the continuum spectrum with the Plank equation. In addition, we examined the propagations of compressional waves in water by shadowgraphy.

This work presents a two-dimensional theoretical model for numerical simulation of femtosecond laser ablation of metals and crater formation, based on the phase explosion mechanism. Parametric studies are carried out to reveal the ablation phenomena with emphasis on the topography formation by a laser pulse. Experiments are also conducted for fs laser ablation of Ni. The results show that the phase explosion model can effectively predict the crater shape as well as the ablation rate in the high-fluence regime where the lattice temperature approaches the spinodal limit.

In this work we investigate the effects on gelatine films of nanosecond pulsed laser irradiation at different laser wavelengths from the UV to the IR at 248, 266, 355, 532 and 1064 nm. We compared gelatines differing in gel strength values (Bloom 75 and 225) and in crosslinking degree. Formation of bubbles at the wavelengths in the UV (248 and 266 nm), melting and resolidification at 355 nm, and formation of craters by ablation in the VIS and IR (532 and 1064 nm) are the observed morphological changes. On the other hand, changes of the fluorescence behaviour of the films upon UV irradiation reveal chemical modifications of photolabile chromophores.

Recently, surface passivated Si nanocrystallites are prepared by pulsed laser ablation (PLA) of Si target in hydrogen gas. Plume analysis during PLA is one of the available methods to clarify a mechanism of surface hydrogenation. We observed plume emission by time- and space-resolved spectroscopy. The dominant species were exited neutral Si atoms and SiH species when the delay time is longer than 100 ns. The Si atoms and SiH species existed throughout the plume. This indicates that nanocrystallites grow in the mixture of Si and SiH vapor. The surfaces of Si nanocrystallites are considered to be hydrogenated by SiH species during the growth. It seems that surface hydrogenation is not due to the spatial separation of Si and H species but due to surface reaction with SiH and/or Si species.

Absorptance change of copper caused by surface modification following multi-pulse femtosecond laser ablation is studied as a function of number of applied laser pulses at various laser fluence. We show that laser-induced surface modification enhances the absorptance due to nano-, micro-, macro-structures and re-deposition of nanoparticles produced by the ablation. At sufficiently high fluence and with a large number of applied pulses, the absorptance of copper following ablation can reach a value of about 85%.

Plasma plume emission spectroscopy signals induced in air by 0.8 mJ of a femtosecond- Single Pulse (fs-SP) laser beam were enhanced by using an orthogonal geometry ns-reheating Dual Pulse (DP) configuration. The plasma plume temperatures of several copper-based-alloy standards and calibration curves of their Sn and Pb contents were conveyed. The resulting data showed an independence from the matrix composition so that, even for significant wt % variation of Sn and Pb, good linear regression coefficients could be obtained (0.99 for Sn and 0.98 for Pb). The DP configuration, here reported, using a low energy (0.8 mJ) of the fs ablating laser beam, was considered for determining the Sn and Pb elemental contents of ancient copper-based-alloy artwork fragments coming from the 'Canne della Battaglia' archaeological site of Minervino Murge (Apulia – South of Italy). The results showed that, even by employing this low energy of the fs laser, which did not cause any visible damage of the ancient samples, the DP configuration supplied large enhancements and very well resolved emission lines of spectra providing information about the Sn and Pb contents which could support archaeologists work.

We have produced crater depths of less than 10 nanometers using 100-1000 pulses of a near-infrared femtosecond laser (800 nm, 125 fs) on a copper thin film surface. By determining the single-shot ablation threshold, incubation coefficient and surface reflectivity, the femtosecond laser pulse parameters for surface nanomilling are established close to the multiple-pulse ablation threshold limit for a copper thin film. Photomultiplier measurements of a copper emission line were used as a real time monitor of the nanomilling process for which photons were detected only once every several shots. The results are consistent with a model that ablation occurs in bursts every several shots after a number of intervening incubation energy storage shots.

The characteristics of thermionic emission of metal films during ultrashort pulse laser ablation are investigated by numerical simulation. The two-temperature model is used to calculate the electron and lattice temperatures while thermionic emission is incorporated into the model as a surface phenomenon. The Richardson-Dushman equation is employed to estimate the rate of thermionic electron emission. The influence of laser irradiance and the film thickness on the emission rate is examined. The change of quantum efficiency is predicted and compared with reported experimental data. The evolution of electron and lattice temperatures and the variation of relaxation time are also investigated in accordance with thermionic emission.

In this work, we investigate the use of Remote Plasma Assisted PLD for the growth of chromium oxide thin films. In an attempt to enhance oxygen incorporation in the growing layers, laser ablation takes place in an activated oxygen background that contains atomic oxygen as well as excited oxygen molecules, thereby creating growth conditions that are inaccessible by reactive PLD. All films were grown on Si (100) substrates by ablating a pure Cr₂O₃ target using a KrF excimer laser. The micro-structural analysis of the grown layers was achieved using Infra- Red Spectroscopy, X-Ray Diffraction, Atomic Force Microscopy and Rutherford Back- Scattering. It is found that films deposited under remote plasma conditions show a predominance of the higher oxidation states of chromium while the antiferromagnetic Cr₂O₃ phase is mostly present in films grown in an O₂ ambient. The effect of substrate temperature on the microstructure of the films was also studied. At low substrate temperatures (<350°C), the films have an amorphous microstructure with elongated rod-like features that could indicate the formation of the CrO₂ phase. With increasing temperature up to 450oC, the structure of the films reverts to a crystalline Cr₂O₃ phase as inferred from the appearance of the corresponding peaks in the XRD spectra and from the narrowing of the infra-red absorption bands.

The influence of surface irradiation of GaAs with a KrF excimer laser on the magnitude of the quantum well intermixing (QWI) effect has been investigated on GaAs/AlGaAs and GaAs/AlGaAs/InAlGaAs QWs heterostructures. The selective area irradiation through a SiO_x mask was carried out in an atmospheric environment. Following the 1000 pulses irradiation at 100 mJ/cm², the samples were annealed in a rapid thermal annealing furnace at 900 °C. Photoluminescence mapping and cathodoluminescence measurements show that significant laser-induced suppression of the QWI process can be achieved with lateral resolution of the order of 1μm.

We have investigated the ablation behaviour of single crystal SrTiO₃ <100> with focus on the influence of the pulse duration at a wavelength of 248 nm. The experiments were performed with KrF-excimer lasers with pulse durations of 34 ns and 500 fs, respectively. Femtosecond-ablation turns out to be more efficient by one order of magnitude and to eliminate the known problem of cracking of SrTiO₃ during laser machining with longer pulses [1],[2]. In addition, the cavities ablated with femtosecond pulses display a smoother surface with no indication of melting and well-defined, sharp edges. These effects can be explained by the reduced thermal shock effect on the material by using ultrashort pulses.

Pulsed laser ablation from a rotating graphite target operating both in vacuum (∼10-5 Pa) and in He sustaining gas (∼10 Pa) has been used to grow thin carbon films on Si <100>substrates kept at temperatures from RT to 900 °C. Synchrotron and laboratory X-ray diffraction (XRD), performed at grazing incidence, established the formation of nano-sized graphene structures at higher deposition temperatures (∼800 ÷ 900°C). When the carbon plume was expanding in vacuum, these structures resulted to be formed by few parallel graphene layers, characterised by an oriented growth along the graphene planes, with the axis parallel to the substrate. High resolution (HR) cross section TEM images of C nano-structures on grids or in film/Si substrate confirmed both size and orientation of the graphene nano-particles. The presence of He atmosphere in the reaction chamber changes basically the particle nucleation process: a clustering phenomenon of aromatic structures is promoted in the gas phase also at low temperature. The nano-structured particles, however, are characterised by a round shaped morphology and random orientation. The mass density of deposited films, measured by X-ray reflectivity, is also strongly dependent on the experimental settings: films grown in the inert gas show lower density compared to the vacuum deposited ones. The preferential vertically oriented growth of graphene layers in vacuum and high temperature can be explained as a combined effect of different processes under a fast kinetic mode: thermal surface diffusion, in-plane growth of graphene sheets and line source direction of activated carbon species of the laser plume. He deposited samples are characterised by a different nucleation and growth process and a more complex structure.

The ablation products of various polymers (triazene polymers, polyimides and glycidyl azide polymer) with 157 nm F₂ laser irradiation were studied with time-of-flight mass spectroscopy, ion probe and white-light interferometry. In contrast to the ablation with longer UV wavelengths, 157 nm irradiation results in non-preferential bond-breaking and a much more pronounced fragmentation into fragments with masses <50 amu. This result suggests a photochemical ablation process that occurs at any bond in the molecule. In addition, ions have been detected at very low fluence similar to the threshold of neutral detection, which is below 30 mJcm⁻² for the triazene polymers and Kapton. The observation of ions from the onset of ablation suggests a 2-photon ablation mechanism and possibly involves an excited neutral as an intermediate step. The low thresholds were verified by ion probe measurements of the ablation plume and white-light interferometry of the ablated target surface.

Deposited films were prepared by ablation of disk-like targets of 3,4,9,10- perylenetetracarboxylic dianhydride (PTCDA) and mixed targets of PTCDA with cobalt (PTCDA-Co) and copper powders (PTCDA-Cu) using the third harmonic of a Nd:YAG laser (355 nm) at fluences ranging from 0.1 to 1.0 Jcm⁻²pulse⁻¹. FT-IR and Raman spectroscopy showed that ablation of PTCDA-Cu at more than 500 mJcm⁻²pulse⁻¹ led to an effective elimination reaction of the anhydride groups of PTCDA as well as PTCDA-Co at more than 700 mJcm⁻²pulse⁻¹. In ablation of PTCDA-Co and PTCDA-Cu, plasma emission was observed around 500 nm. With increasing fluence, addition to the plasma emission, peaks at 437, 469, 513 and 550 nm coming from C₂ radicals were observed, suggesting that PTCDA was partially decomposed into C₂. TOF mass spectra in ablation of PTCDA-Co showed fragments of PTCDA without one or two anhydride groups as well as CoC_n⁺ (n = 0-5) and Co (CO)₂⁺.

Usually ferroelectric thin films are deposited by pulsed laser deposition (PLD) at elevated substrate temperatures, in order to obtain a good crystalline quality. Here we report the fabrication of ferroelectric BaTiO₃ and BiFeO₃ structures by room-temperature PLD combined with post-deposition annealing, and their ferroelectric characterization. A method to control the position of the deposited structures is also presented.

A hydrodynamic model based on transport equations and semi-empirical multiphase equations-of-state for metals is developed and applied to simulation of short pulse laser melting and resolidification. New computational algorithms are developed for modeling of two-phase zones of solid-liquid and liquid-gas coexistence, as well as for explicit tracking of interfaces between the phases. The model accounts for both heterogeneous and homogeneous melting mechanisms. A series of simulations are performed for bulk aluminum irradiated by a picosecond laser pulse at a wide range of laser fluence. The effect of non-equilibrium conditions and homogeneous melting on the melting/resolidification times and the maximum depth of melting is investigated. Three distinct stages are identified in the melting/resolidification process, namely, the fast homogeneous melting of the overheated surface region, a slower increase of the melting depth due to the advancement of the sharp melting front formed at the end of the homogeneous melting, and the reverse propagation of the liquid-crystal interface in recrystallization. Computational results are in a good qualitative agreement with the results of recent molecular dynamics simulations of laser melting.

The propagation of ultrashort laser pulses in dense optical media is investigated theoretically by solving numerically the nonlinear Schrödinger equation. It is shown that the maximum energy density deposition as a function of the pulse energy presents a well-defined threshold that increases with the pulse duration. As a consequence of plasma defocusing, the maximum energy density deposition is generally smaller and the size of the energy deposition zone is generally larger for shorter pulses. Nevertheless, significant values of the energy density deposition can be obtained near threshold, i.e., at lower energy than for longer pulses.

Poly(amic acid) (PAA), a precursor to polyimide, was successfully deposited on substrates without reaching curing temperature, by resonant infrared pulsed laser ablation. The PAA was prepared by dissolving pyromellitic dianhydride and 4, 4' oxidianiline in the polar solvent Nmethyl pyrrolidinone (NMP). The PAA was deposited in droplet-like morphologies when ablation occurred in air, and in string-like moieties in the case of ablation in vacuum. In the as-deposited condition, the PAA was easily removed by washing with NMP; however, once cured thermally for thirty minutes, the PAA hardened, indicating the expected thermosetting property. Plume shadowgraphy showed very clear contrasts in the ablation mechanism between ablation of the solvent alone and the ablation of the PAA, even at low concentrations. A Wavelength dependence in plume velocity was also observed.

A laser ablation/ionization mass spectrometer system is described for the direct chemical analysis of solids. An Nd:YAG laser is used for ablation and ionization of the sample in a quadrupole ion trap operated in an ion-storage (IS) mode that is coupled with a reflectron time-of-flight mass spectrometer (TOF-MS). Single pulse experiments have demonstrated simultaneous detection of up to 14 elements present in glasses in the ppm range. However, detection of the components has produced non-stoichiometric results due to difference in ionization potentials and fractionation effects. Time-of-flight secondary ionization mass spectrometry (TOF-SIMS) was used to spatially map elemental species on the surface and provide further evidence of fractionation effects. Resolution (m/Δm) of 1500 and detection limits of approximately 10 pg have been achieved with a single laser pulse. The system configuration and related operating principles for accurately measuring low concentrations of isotopes are described.

Commercially Pure Titanium foils, were irradiated using a pulsed Nd:YAG laser under ambient air, in order to produce and characterize a well controlled surface texture (roughness and waviness) that enhances osseointegration. To study the 'peri-implant' reparative process response, the laser treated Ti foils were implanted in the tibia of 10 male Wistar rats. At 14 days post-implantation, the histological analysis showed a tendency to more bone formation compared to the untreated control implants. The formation of a layer of TiN on the surface and the obtained roughness, have been demonstrated to improve bone response.

Microstructure formation of cone-like protrusions (CLP) on titanium (Ti) plate by the femtosecond laser ablation is reported. The number of the laser pulses to irradiate the Ti plate was varied from 10 to 230 at average laser fluence of 0.75 J/cm² per pulse on the plate. The onset of CLP creation was observed with exposure of 70 pulses, and yielding CLP with a height from the bottom of the irradiation area of about 9 m after 230 pulses. The formation process of the CLP was found to depend on the laser produced periodic microstructures oriented parallel to the direction of the laser polarization vector.

We report on structural and optical properties for Zn_1-xMg_xO (ZMO) thin films produced by pulsed laser ablation. ZMO thin films were grown on a-plane Al₂O₃ substrates at 400°C. In order to efficiently incorporate Mg into ZnO thin films, we used multiple ZnO-MgO ablation targets. Pulses from a Nd:YAG laser (4th harmonic generation: 266 nm) were directed on the ZnO-MgO ablation targets, which consisted of MgO single crystals mounted on ZnO ceramic targets. The ZMO films were characterized by x-ray diffraction, optical transmittance and cathodeluminescence (CL) measurements. Highly c-axis oriented ZMO(0002) reflections corresponding to the wurtzite-phase were observed. The c-axis lattice constants of the films were determined from the ZnMgO(0002) peak. The c-axis length of the ZMO films decreased linearly with Mg content. From the optical transmittance spectra of ZMO films, we observed a blue shift in the absorption edge with increasing Mg content. Band gap energies of ZMO thin films were determined from the optical transmittance and CL spectra. We found that the band gap energy changed from 3.27 eV to 3.95 eV. The Mg content of ZMO films increased monotonically with the number of laser pulses which struck the MgO target. These results show that laser ablation using multiple targets of ZnO and MgO is effective for band engineering of ZMO.

In this work, the shape of a near-field scanning optical microscopy (NSOM) probe was modified using the results of numerical analysis based on a finite-difference time-domain (FDTD) algorithm. This probe has a narrow slit or small tip on its aperture. Especially in the near-field area, the electric field intensity distribution is heavily dependent on the polarization of the incident light. In the plane of polarization, the electric field intensity of the NSOM aperture probe is strongly enhanced at the edge of the aperture. Simulation results show that this enhancement can be totally or partially removed according to the size of the slit, if the slit carved on the probe is aligned with the polarization direction of the incident light. When a long slit is carved on the probe, the electric field intensity of the NSOM aperture probe in the plane of polarization shows a Gaussian distribution because the points of enhanced electric field intensity are totally removed. However, when a short slit is carved on the probe, the point of enhanced electric field intensity is removed at one edge of the aperture, and consequently the electric field intensity is enhanced only at the other edge. Moreover, when a tip is put on the probe, the electric field intensity is enhanced only near the tip. This means that a higher intensity electric field can be obtained on the surface to be processed in an area smaller than the aperture size. Therefore, the modified probe is expected to improve the fabrication of extremely small patterns. Furthermore, this type of probe can be easily realized compared to any other new-type probes, because it can be manufactured directly from existing probes.

We report measurements of laser-induced photoelectron emission (LIPEE) from single crystal aluminum (99.999%) and high purity polycrystalline aluminum (>99.9%) during uniaxial tensile deformation. A 248-nm excimer laser (5-eV photon energy) was used as a light source. Deformation was performed on a tensile stage in ultra-high vacuum at an initial strain rate of 1 × 10⁻³ s⁻¹. Photoelectron intensities are sensitive to changes in surface morphology accompanying deformation, including slip line and band formation. In the single crystal material, LIPEE intensity initially increases linearly with strain followed by a monotonically decreasing slope at larger strain. In the polycrystalline material, LIPEE intensities increase linearly with strain in two segments. Slip bands on the deformed surfaces were characterized by atomic force microscopy (AFM).

During high repetition rate (>200 kHz) ultrafast laser waveguide writing, visible heat modified zones surrounding the formed waveguide occur as a result of heat accumulation. The radii of the heat-modified zones increase with the laser net fluence, and were found to correlate with the formation of low-loss and cylindrically symmetric optical waveguides. A numerical thermal model based on the finite difference method is applied here to account for cumulative heating and diffusion effects. The model successfully shows that heat propagation and accumulation accurately predict the radius of the 'heat modified' zones observed in borosilicate glass waveguides formed across a wide range of laser exposure conditions. Such modelling promises better control of thermal effects for optimizing the fabrication and performance of three-dimensional optical devices in transparent materials.

We demonstrate colour marking of a transparent material using laser-induced plasma-assisted ablation (LIPAA) system. After the LIPAA process, metal thin film is deposited on the surface of the ablated groove. This feature is applied to RGB (red, green and blue) colour marking by using specific metal targets. The metal targets, for instance, are Pb₃O₄ for red, Cr₂O₃ for green and [Cu(C₃₂H₁₅ClN₈)] for blue colour marking. Additionally, adhesion of the metal thin film deposited on the processed groove by various experimental conditions is investigated.

A deep ultraviolet F₂ laser, with output at 157-nm wavelength, has been adopted for micro-shaping the end facets of single and multi-mode silica optical fibres. The high energy 7.9-eV photons drive strong interactions in the wide-bandgap silica fibres to enable the fabrication of surface-relief microstructures with high spatial resolution and smooth surface morphology. Diffraction gratings, focusing lenses, and Mach-Zehnder interferometric structures have been micromachined onto the cleaved-fibre facets and optically characterized. F₂-laser micromachining is shown to be a rapid and facile means for direct-writing of novel infibre photonic components.

The 157nm F₂-laser drives strong and precisely controllable interactions with fused silica, the most widely used material for bulk optics, optical fibers, and planar optical circuits. A diffractive optical element (DOE) breaks apart wavefronts and redirects segmented beamlets through phase control for novel beam steering and shaping applications. This paper shows that precise excisions of 10-30 nm depth are available from the F₂ laser for the generation of efficient DOEs for the visible and ultraviolet spectrum. F₂-laser radiation was applied with beam homogenization optics and high-precision computer-controlled motion stages to shape up to 16-level, 256 × 256 pixel DOE devices on bulk glasses, with distinguishable level-tolevel spacing of ∼100 nm and surface roughness of ∼13 nm. The 1st order diffraction efficiency was ∼35%. The farfield pattern when illuminated with a HeNe laser was found to agree with simulations based on an iterative Fourier transform algorithm. Future improvements in the laser micromachining process and possible directions are also offered.

Laser micromachining technology is a cost-effective microfabrication technique for prototyping and in some cases batch production of miniature components and microdevices with complex geometries requiring high accuracy and precision. The objective of this paper is to analyze experimentally the effect of the laser micromachining process and its parameters, particularly, the pulse duration, on the characteristics of the fabricated functional microdevices. This was achieved through the microfabrication of two electro-thermally driven in-plane microactuators using a femtosecond and a nanosecond pulse laser. The dynamic/static performance of the microactuators was compared with respect to the required current/power and generated actuation force/displacement and the geometric quality of the machining.

Finer and cleaner features are expected in micro-machining with high power, ultrashort pulse lasers as the melt and evaporation phases are considerably reduced. However, a high-intensity optical beam propagating through a gaseous medium can cause its breakdown generating plasma, which is enhanced further by the self focusing effect of the medium. Photon-plasma scattering compensates somewhat for the self-focusing, but it also distorts the beam profile with consequent impact on the fabricated surface. Plasma also continues to supply heat beyond the pulse duration, which may cause melting and thus distort the features further. In the present article, we show that suitable parameters can be determined to reduce the distortion to the beam profile and balance self-focusing and plasma defocusing resulting in plasma filamentation. Well-shaped beam and plasma filaments, both have favourable impact on the fabricated features. The calculated surface features are compared with the experimentally machined crater profiles with good agreement.

Photochemical writing of silica (SiO₂) optical waveguides in silicone [(SiO(CH₃)₂)_n] rubber has been successfully demonstrated by 157-nm F₂ laser-induced photochemical modification of silicone into silica. The 2-mm-thick or ∼40- m-thick silicone rubber was exposed to F₂ laser through a thin (∼0.2 mm) air layer. A proximity Cr-on-CaF₂ photomask with 8- to 16- m-wide slits controlled the exposure size to define the width of the silica waveguides. A laser processing window to generate crack-free waveguides with good optical transparency was found by varying the number laser pulse, pulse repetition rate and single pulse laser fluence. Otherwise, rapid or excess exposure of the F₂ laser caused cracking of the silica waveguides. The waveguides were found to guide both red (635-nm) and infrared (1550- nm) wavelength light with propagation loss estimated to be ∼15 and ∼6 dB/cm, respectively. Most of the loss originates in Rayleigh scattering from numerous inclusions originally present in the commercial 2-mm-thick silicone rubber.

Photochemical welding of fused silica glass to silicone rubber has been demonstrated by 157-nm F₂ laser-induced photochemical modification of the silicone surface in contact with the glass. Fused-silica coverslips (150 m thick), silica optical fibres (125 µm diameter), and 2.9- µm diameter microspheres were successfully welded onto 2-mm-thick silicone rubber by irradiating the silicone surface through the partially transparent glasses. Sufficient photochemical conversion for strong welding was provided by multiple exposures of tens to thousands of pulses in a narrow optimized fluence window near ∼6-mJ/cm² per pulse.

An improvement in morphology, crystallinity, and optical property of ZnTe nanoparticles produced by pulsed laser ablation (PLA) was achieved by in situ annealing. ZnTe nanoparticles produced in argon gas ambience by PLA were annealed in the gas flow at a temperatures T_a ranging from 300 °C to 800 °C and size-selected by a differential mobility analyzer. The bimodal size distribution of the ZnTe nanoparticles changed to unimodal at T_a = 600 °C. In this condition, the shape of the monodispersed ZnTe nanoparticles, classified into around 20 nm, became uniformly spherical and their crystallinity estimated by x-ray diffraction was extremely improved. These improvements by the in situ annealing were examined for ZnTe nanoparticles produced from off-stoichiometric target. Although the optical property of ZnTe nanoparticles produced from a zinc rich target was improved, those produced from a tellurium rich target could not be improved. It was found that the effect of in situ annealing on optical properties of ZnTe nanoparticles was dependent upon its content.

Plasma plume induced by ArF excimer laser during the ablation of a hydroxyapatite (Ca_1O(PO₄)₆(OH)₂) target is studied in different ambient conditions., i.e in air or water vapour. It is found that the plasma shape and plasma front velocities strongly depend on the ambient pressure. Appropriately selected reactive atmosphere enhances also the layer growth process.

Thin films of the amino-acids phenylalanine (Phe) and tyrosine (Tyr) were prepared by PLD with a KrF laser at fluences of some hundreds mJ/cm². Conservation of the chemical structure and a metastable modification of the molecular interactions are evidenced by IR spectroscopy. The evolution of the refractive indices with fluence was correlated with the structure determined by X ray diffraction. Phe plume expansion imaging was achieved.

The interaction between two plasmas induced by cross-beam pulsed laser ablation onto two perpendicular graphite targets was analyzed by time resolved optical emission spectroscopy. Ablation was performed by excimer (248 nm) and Nd: YAG (1064 nm) synchronized lasers, delayed up to 40 µs. The kinetic energy of the second pulse species can be controlled by changing the pulse delay between lasers or increasing the energy of the first pulse. Furthermore an increase of emitting C III and a decrease of neutrals was observed. This is due to plasma interaction causing excitation processes over the second plume.

Reaction of benzene molecules with ablated silicon ions and neutrals were investigated by space- and time-resolved optical emission spectroscopy. The time-resolved emission spectrum showed production of excited C₂ and CH radicals after 180-ns delay from laser irradiation. Comparing the temporal evolution of C₂* with that of Si*, we concluded that the neutral Si atoms contribute to the production of the C₂ radicals. The emission in a mixture of benzene vapor and neon gas suggested that the neutral Si atoms could excite the buffer atoms and molecules to high-energy levels. Based on the result, the production process of the C₂ radicals is discussed.

We present a summary of initial work on the etching of silica at 157 nm. At fluences well below the threshold for plasma formation, we have characterized the direct desorption of atomic ions from fused silica surfaces during 157-nm irradiation. The ion identities and kinetic energies were determined by time-resolved mass spectroscopy. The principal ions are Si⁺ and O⁺. The emission intensities are dramatically increased by treatments that are expected to increase the density of surfaces defects. Molecular dynamics simulations of the silica surface suggest that silicon ions bound at surface oxygen vacancies (analogous to E' centers) provide suitable configurations for emission. We propose that emission is best understood in terms of a hybrid mechanism involving both antibonding chemical forces (Menzel-Gomer-Redhead model) and repulsive electrostatic forces on the adsorbed ion after laser excitation of the underlying defect.

Pulsed UV laser processing is used to drill micro holes in silicon carbide (SiC) wafers supporting AlGaN/GaN transistor structures. Direct laser ablation using nanosecond pulses has been proven to provide an efficient way to create through and blind holes in 400 µm thick SiC. When drilling through, openings in the front pads are formed, while blind holes stop ∼40 µm before the backside and were advanced to the electrical contact pad by subsequent plasma etching without an additional mask. Low induction connections (vias) between the transistor's source pads and the ground on the backside were formed by metallization of the holes. Micro vias having aspect ratios of 5-6 have been processed in 400 µm SiC. The process flow from wafer layout to laser drilling is available including an automated beam alignment that allows a positioning accuracy of ±1 µm with respect to existing patterns on the wafer. As proven by electrical dc and rf measurements the laser-assisted via technologies have successfully been implemented into fabrication of AlGaN/GaN high-power transistors.

This work highlights a potential pitfall associated with using optical emission to estimate the expansion velocity of material in laser ablation plumes, speci.cally when the monitored emission involves transition to a state that is present in high number density. Comparisons of time-gated, spatially resolved, images of the Li(3d. 2p) and Li(2p. 2s) emissions arising in the nanosecond 248 nm pulsed laser ablation of LiF enabled estimation of the distribution of ground state Li atoms in the plume. Analysis of these images revealed that the density of Li(2p) atoms in the early stages of the plume expansion was su.ciently high that even the Li(3d → 2p) emission profiles show evidence of radiation trapping.

In this study, the spatial distribution of laser induced transient stress wave have been observed successfully by both shadowgraph and photoelasticity images using transparent materials. It has been found that photoelasticity images of polymer materials, such as epoxy resin, observed in laser irradiation under water provide clear images which would allow quantitative estimation of the magnitude of laser induced stress. Obtained photoelastic images show clear black-and-white patterns from which laser-induced stress distribution and its dynamical change can be deduced. When a metal film was coated on the surface of an epoxy block, obtained images from the sample indicate the interaction of laser with the metal surface. A semi-quantitative estimation of intensity of the laser-surface interaction has been carried out by comparing images to those obtained for designated pulse energies.

A time resolving Langmuir probe was used to study the plasma plumes produced by the ablation of Ag, Ni and Al targets with laser pulses of different pulse durations (0.2 − 10 ps). These metals were chosen because their electron-phonon relaxation times, τ_e-ph, are of the order of the pulse durations used. The time of flight (TOF) signals have been used to establish the threshold fluences and plume expansion dynamics of the laser produced plasmas for the different pulse durations. The angular dependence of the magnitude of the ion flux was analysed on the basis of Anisimov's self-similar model of the plasma expansion. The amount of charge in the ablation plume is compared for the different pulse durations.

In the development of extreme ultraviolet (EUV) sources for practical optical lithography systems, one of the most important subjects is debris mitigation. In, particularly mitigation of fast neutral atoms is very difficult compared with other particles such as ions and droplets. Thus, in our study, we developed a visualization system for neutral atoms emitted from laser-produced plasma (LPP) based EUV source using a laser induced fluorescence (LIF) method and investigated neutral debris behaviors in order to obtain the guideline for the optimization of debris shields. In the present measurement system, neutral atoms with a kinetic energy of less than 200 eV could be detected at a pump fluence of about 4 102 J/cm² using a solid tin target. The interaction between the fast ions and substrate was also observed by the LIF system

We demonstrate experimentally and describe theoretically the formation of carbon nanoclusters created by single picosecond laser pulses. We show that the average size of a nanocluster is determined exclusively by single laser pulse parameters and is independent of the gas fill (He, Ar, Kr, Xe) and pressure in a range from 20mTorr to 200 Torr. Simple kinetic theory allows estimates to be made of the cluster size, which are in qualitative agreement with the experimental data. We conclude that the role of the buffer gas is to induce a transition between thin solid film formation on the substrate and foam formation by diffusing the clusters through the gas, with no significant effect upon the average cluster size.

Abstract. We developed a space- and time-resolved soft x-ray absorption spectroscopy system for the study of ablation dynamics induced by femtosecond laser irradiation onto an aluminum target. The system consists of an x-ray microscope for imaging and a femtosecond-laserplasma x-ray source for time-resolved measurements. Ablation of neutral and condensed aluminum particles following plasma expansion was observed as shifts of the aluminum L-shell photoabsorption edge in space- and time resolved absorbance spectra.

Time dependent behavior of laser-produced tin plasma has been investigated using gated optical emission spectroscopy. Plasma was generated by focusing 1.064 m Nd:YAG laser light onto a solid density, planar tin target in vacuum at a laser irradiance of 3.8 × 10¹¹ W/cm². Estimates of the electron temperature and density were made by assuming Boltzmann distributed population levels and Stark broadened singly ionized tin spectral lines, respectively. An initial temperature of 1.4 eV and density of 4.1 × 10¹⁷ cm⁻³ were calculated from the analysis of spectral data. Experimental data were interpreted alongside numerical results from HYADES - a onedimensional radiation hydrodynamics plasma simulation code. An energy balance was calculated to determine the fraction of incident laser energy converted to directed kinetic energy of expansion.