Table of contents

In this paper, we report how to realize an all-solid-state laser with an efficient dual-wavelength red and green light output by temperature tuning. This laser is constructed with a nonlinear crystal and a diode-pumped, Q-switched Nd : YVO₄ laser as the fundamental source with the dual-resonance wavelengths at 1342 and 1064 nm. The nonlinear crystal is a specially designed superlattice that is able to achieve quasi-phase-matched frequency doubling of 1342 and 1064 nm at two phase-matching temperatures. Using this scheme, 520 mW red light and 332 mW green light are generated at 118.5°C and 113°C, respectively, from two moderate fundamental powers with an efficiency of around 25–30%. The results provide a possible scheme for obtaining multi-wavelength output from a mono-laser by only adjusting the operating temperature.

a-Axis oriented La_0.8Na_0.2MnO₃ (LNMO) and La_0.8Na_0.2Mn_0.95Cu_0.05O₃ (LNMCO) films with large magnetoresistance (MR) near room temperature are fabricated via chemical solution deposition on yttrium-stabilized zirconia (YSZ) (1 0 0) single crystal substrates. With slight Cu doping, it is found that the growth mode is changed from the layer-by-layer mode of the LNMO film to the island mode of the LNMCO film. The LNMO film exhibits typical transport properties of epitaxial films of manganites. However, the LNMCO film shows transport properties corresponding to polycrystalline films of manganites. The MR value of the LNMCO film at low applied magnetic field is also remarkably enhanced compared with that of the LNMO film below the insulator–metal transition temperature. MR as high as 9% is obtained at a field of 0.05 T at 5 K. The enhanced MR effect for the LNMCO film is attributed to the spin-dependent scattering of polarized electrons at the grain boundaries.

In this paper the transformation of one type of photostimulable colour centre (F-centre) into another, depending on the preparation conditions of the storage phosphor BaFBr : Eu²⁺, is investigated. Despite the fact that the quasi-binary phase diagram of BaF₂-BaBr₂ shows no detectable solid solution for either BaF₂ or BaBr₂ in BaFBr, it will be demonstrated that an imbalance induced on purpose in the bromine/fluorine ratio can alter the shape of the stimulation spectrum from F(F⁻)- to F(Br⁻)-centres and vice versa in a subsequent annealing process. It will be demonstrated that such an imbalance can be generated by exposing BaFBr : Eu²⁺ to an alcohol/water solution between a sintering step and an annealing step. Thereby the water dissolves BaFBr by removing BaBr₂ from the surface of the grains, leaving an excess of BaF₂ behind. Based on these findings a practical synthesis route will be offered, which can lead to improved phosphor properties. Such properties are a macroscopically single phase of BaFBr : Eu²⁺ without detectable BaF₂ or BaBr₂ residuals and solely photostimulable F(Br⁻)-centres.

Atomistic simulations are performed to investigate the mechanical properties of uniaxial tensile and bending behaviours of double-walled carbon nanotubes. The second-generation reactive empirical bond-order potential and four different van der Waals (vdW) potentials are used to describe bonding and non-bonding atomic interactions, respectively. It is found that the tensile and bending behaviours are insensitive to the choice of vdW potential. It is shown that the effect of the helicity of nanotubes on the elastic modulus and the tensile strength is significant, while the effect of the nanotube diameter is moderate. Our simulations show that the outer tube always reaches its tensile strength first, suggesting the 'sword-in-sheath' failure mechanism. For the bending deformation, a strong non-linearity between the deformation and load is observed at small deformations, while a nearly linear relation is observed at large deformations.

Thermo-elastic laser-generated ultrasound in layered plates has been studied using the finite element method, after considering the temperature dependence of the thermo-physical parameters of the materials. It is confirmed that the temperature dependence of the thermo-physical parameters has a significant influence on thermo-elastically generated ultrasound with high frequencies. Numerical results calculated in two kinds of two-layer system indicate that the features of the surface acoustic wave (SAW) generated are dependent on the thickness of the surface layer. Numerical results from three-layer systems indicate that the skimming surface longitudinal wave is sensitive to the thickness of the surface layer, while the SAW is much more sensitive to the thickness of the bonding layer, and it can be used to extract the thickness parameter of the bonding layer in an effective way.

This paper presents an interferometric method used to check the rotational temperature of the OH free radical obtained using emission spectroscopy. The temperature is extracted from an interferogram via the phase shifting introduced by the refractive index of the studied medium. The refractive index is related to the temperature through the Gladstone–Dale equation and the ideal gas law.

The method is tested on the laminar premixed flame of an oxy-acetylene burner and on the laminar plume of a dc argon plasma torch. The results obtained are compared with those obtained from the UV OH band at 306.357 nm (transition A²Σ, ν = 0 → X²Π, ν' = 0) by emission spectroscopy using the Boltzmann plot method and using a method based on numerical simulated spectra with the amplitude ratios of groups of unresolved rotational lines.

The time-independent ion distributions of variable composition laser-produced Sn plasmas are studied for a wide range of electron temperatures and atomic number densities, the purpose of which is to elucidate the effect that varying the number density of Sn within a mixed species plasma has upon the steady state populations of Sn and its ions. Particular emphasis will be placed on binary mixtures of Sn with Li, C, O or Sm and more specifically the charge states Sn⁸⁺ to Sn¹³⁺ within these mixed plasmas, where it will be assumed that the plasma is optically thin. It is found that using these composites has relatively little effect upon the Sn ion population distributions for plasma atomic number densities of less than approximately 10^19.5 cm⁻³. However, for greater values of number densities the Sn ion populations can be shifted by as much as 10–15 eV for Li mixtures. These results are of particular relevance to current research being carried out on extreme ultraviolet lithographic technologies for the optimization of XUV sources in the 13.5 nm wavelength region, which include composite target investigations.

A modelling study has been performed on the effect of natural convection on the characteristics of a long laminar argon plasma jet issuing into ambient air. In this study the plasma jet is taken to be flowing vertically upwards or downwards, and the combined diffusion coefficient method has been used to treat the diffusion of ambient air into the argon plasma jet. It has been shown that although a temperature difference as large as 10⁴ K is involved in the long laminar plasma jet system, in total the effect of natural convection on the fluid flow and heat/mass transfer within the plasma jet is small for the typical plasma jet parameters under study. Only at low jet inlet velocities and near the jet edge in the jet downstream region can the natural convection effect be detected.

Non-uniformity of ion beam irradiation on a direct-driven heavy ion fusion pellet was studied numerically in our previous paper (2003 Phys. Lett. A 315 372–7). The calculation results demonstrated that a sufficiently low non-uniform energy deposition (<2%) can be realized with a finite number of beams and determined a 32-beam irradiation system as the most interesting for practical application. A more particular analysis of that irradiation scheme is done in this paper. The simulation model is improved, including the temperature growth during the time of irradiation. A study of the beam focusing and beam emittance dependences on the non-uniformity of energy deposition is conducted.

In the presence of a magnetic wiggler of suitable period, a Gaussian laser beam resonantly generates a second harmonic in a plasma. The phase matching conditions for the process are satisfied for a specific value of the wiggler period. The self-focusing of the fundamental pulse enhances the intensity of the second-harmonic pulse. The harmonic undergoes periodic focusing in the plasma channel created by the fundamental wave. The normalized second-harmonic amplitude varies periodically with distance with successive maxima acquiring higher values.

We have investigated the scaling of peak vacuum ultraviolet output power from homogeneous Xe dielectric barrier discharges excited by short voltage pulses. Increasing the Xe fill pressure above 1 bar provides an increased output pulse energy, a shortened pulse duration and increases in the peak output power of two to three orders of magnitude. High peak power pulses of up to 6 W cm⁻² are generated with a high efficiency for pulse rates up to 50 kHz. We show that the temporal pulse characteristics are in good agreement with results from detailed computer modelling of the discharge kinetics.

The recently developed broad-band absorption technique of 'mode-locked cavity-enhanced absorption spectroscopy' (ML-CEAS) is applied to the diagnostics of argon and nitrogen plasmas. Using a commercial tunable mode-locked Ti : Sa femtosecond laser, this combines the multipass advantage of the cavity-enhanced technique with the simultaneous acquisition over a broad spectral range of classic broad-band absorption spectroscopy. Absorption spectra in the 400 nm range are acquired after frequency doubling of the Ti : Sa femtosecond laser in a BBO crystal. The measurement of the metastable Ar^*(³P₂) atom density in a low pressure argon glow discharge through its weakly absorbing lines at 394.75 and 394.898 nm allows us to illustrate the importance of the apparatus' spectral resolution for determination of absolute number densities. Absorption spectra of the first negative band of the nitrogen ion, , around 391 nm are recorded in a nitrogen glow discharge and in the afterglow of a flowing μ-wave nitrogen plasma. The absolute ion density (and its rotational temperature) measured in the discharge zone and in the maximum of the short-lived afterglow (SLA) are 1.5 × 10¹⁵ ions m⁻³ (1300 K) and 1.0 × 10¹⁵ ions m⁻³ (800 K), respectively. Compared with the previously measured electron density at the maximum of the SLA, it is concluded that ions are not the dominant positive ions in this zone.

Diamond-like carbon (DLC) films were deposited on a Si substrate by electrolysis in a methanol solution at ambient pressure and low temperature. The morphology and microstructure of the resulting DLC films were analysed using atomic force microscopy, Raman spectroscopy, Fourier transformation infrared spectrometry, x-ray photoelectron spectroscopy (XPS), and x-ray excited Auger electron spectroscopy (XAES). The surface energy and mechanical properties of the DLC films were examined, and the growth mechanism of the DLC films in liquid phase electro-deposition is discussed as well. The results of the study show that the hydrogenated diamond-like carbon films are smooth and compact. The percentage of sp³ carbon in the DLC films is determined as 55–60%, based on the corresponding XPS and first-derivative XAES spectra of graphite, diamond, and the tested films. The DLC films show low surface free energy, good mechanical properties, excellent friction–reduction and wear-resistance. It is suggested that methanol dissociates to generate the active species of and C₂H₄ at high voltage applied to the electrode, followed by the generation of the alkyl chain [–CH₂–CH₂–]_n whose C–C and C–H bond lengths and C–C–C and H–C–H bond angles are close to that of diamond. Subsequently, a diamond-like structure was formed by the ordered dehydrogenation of a short-chain [–CH₂–CH₂–]_n in the electrolysis process.

Preparation of high quality SiO₂ and SiOF films has been attempted from tetraethoxysilane (TEOS)/O₂ and TEOS/O₂/CF₄ precursors by modifying deposition variables. The deposited films were fully characterized by various analytical tools, such as FT-IR, UV-VIS-NIR spectrophotometry, XPS, ex situ ellipsometry and SEM. From the characterization of SiO₂ films, it was demonstrated that the TEOS/O₂ flow ratio is a critical parameter that controls the film quality and, when the TEOS/O₂ flow ratio is low enough to prevent the physical adsorption of TEOS on the film surface during growth, good quality SiO₂ films can be deposited at a high growth rate, even at low temperatures of 100°C. It is also noted that the addition of CF₄ ranging from 0 to 70 sccm to the TEOS/O₂ mixture can induce a lowering of the refractive index by replacing the highly polarizable Si–OH and OH bonds with less polarizable Si–F bonds and result in the formation of an SiOF film having good optical and structural characteristics without disadvantages such as a porous structure and hygroscopicity.

Artificial heterostructures alternated by tetragonal and rhombohedral phases have been introduced into two-dimensional (2D) relaxor (1−x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ thin films as one-dimensional (1D) superlattices. Spontaneous polarization coupling between the two phases was observed and attributed to both the natural existence of nano-features in ferroelectric relaxors and the slightly distorted crystalline structure in superlattices with much reduced internal strains. The dielectric constant increased by more than 50% and the out-of-plane electro-optic coefficient improved by more than one order of magnitude because of this coupling. These results demonstrate that these nano-scale heterostructures can be introduced into 1D and 2D complex oxide materials for various photonic applications.

The electronic mechanisms induced by the UV exposure of thin films of polyvinyl alcohol doped with pairs of mixed valence metal ions were studied in relation to their optical behaviour by Mössbauer spectroscopy and optical absorption. The results obtained definitely point to the role of each element from the pair in the electronic mechanism involved, with influence on the optical properties regarding applications in real-time holography and integrated optics.

Luminescence of Eu³⁺ in Pb(Zr_xTi_1−x)O₃ (PZT) polycrystalline tetragonal samples synthesized by sol–gel processing is reported. Studies by x-ray diffraction, energy dispersive spectroscopy and high resolution transmission electron microscopy demonstrate the incorporation of the dopant in the host. A broad charge transfer band centred around 266 nm was observed in the Eu³⁺ excitation spectra. Eu³⁺ is in a low symmetry site. Luminescence was lost between 673 and 1173 K. It was recovered after 1 h of heat treatment at 1273 K, when nanocrystallites were formed.

Copper wafers are polished with an experimental slurry prepared to contain strong oxidizing components for revealing grain structures. Two types of surface morphologies, twinned and equiaxed grains, are observed on two groups of wafers, following chemical mechanical planarization (CMP). An atomic force microscope surface analysis indicates that the equiaxed grain structure provides better overall surface quality than the twinned structure. A polishing model is proposed to explain the surface relief among the twinned subgrains. The results suggest that Cu electroplating and the subsequent annealing processes should be optimized to promote uniform equiaxed grains for better integration with CMP and other chip manufacturing processes.

The machining process of transparent materials using the laser induced backside wet etching (LIBWE) procedure was studied. In the course of this, experimental investigations and numerical calculations were carried out. Fused silica plates were irradiated by an ArF excimer laser, using a naphthalene–methyl methacrylate solution as an absorbing liquid (concentration 0.85 mol dm⁻³, absorption coefficient at 193 nm 52 200 cm⁻¹). The etch rate dependence on the applied laser fluence (varied from 110 to 860 mJ cm⁻²) was derived from the etch depths, measured using an atomic force microscope (AFM). The etch rate was found to be 4.7–49.5 nm/pulse, depending on the laser fluence. The surface morphology of the etched edges was also investigated by AFM. A fast photographic arrangement was used for time resolved observation of bubble development in the liquid absorbent, which is an important phenomenon of LIBWE. The internal pressure of the expanding bubbles was calculated using recorded snapshots. It was found to be 22–120 MPa 17.2 ns after the excimer pulse peak. The one-dimensional heat flow equation, including the melting of the treated fused silica layer and the vaporization of the absorbing solution, was solved using the finite difference method. The surface temperature of the fused silica was found to be a maximal 17.2 ns after the excimer pulse peak. Based on our results, we present a possible interpretation of the LIBWE procedure of fused silica.

O₂(a ¹Δ_g) production in a non-self-sustained discharge (ND) in pure oxygen and oxygen mixtures with inert gases (Ar and He) has been studied. A self-consistent model of ND in pure oxygen is developed, allowing us to simulate all the obtained experimental data. Agreement between the experimental and simulated results for pure oxygen over a wide range of reduced electric fields was reached only after taking into account the ion component of the discharge current. It is shown that the correct estimation of the energetic efficiency of O₂(a ¹Δ_g) excitation by discharge using the EEDF calculation is possible only with the correct description of the energy deposit into the plasma on the basis of an adequate discharge model. The testing of an O₂(a ¹Δ_g) excitation cross-section by direct electron impact, as well as a kinetic scheme of processes involving singlet oxygen, has been carried out by the comparison of experimental and simulated data. The tested model was then used for simulating O₂(a ¹Δ_g) production in ND in oxygen mixtures with inert gases. The study of O₂(a ¹Δ_g) production in Ar : O₂ mixtures with small oxygen content has shown that the ND in these mixtures is spatially non-uniform, which essentially decreases the energetic efficiency of singlet oxygen generation. While simulating the singlet oxygen density dynamics, the process of three-body deactivation of O₂(a ¹Δ_g) by O(³P) atoms was for the first time taken into account. The maximal achievable concentration of singlet oxygen in ND can be limited by this quenching. On the basis of the results obtained and the model developed, the influence of hydrogen additives on singlet oxygen kinetics in argon–oxygen–hydrogen mixtures has been analysed. The simulation has shown that fast quenching of O₂(a ¹Δ_g) by atomic hydrogen is possible due to significant gas heating in the discharge that can significantly limit the yield of singlet oxygen in hydrogen-containing mixtures.