Table of contents

An erbium-doped fiber laser based on random distributed feedback through Rayleigh scattering in a long-distance (5–30 km) single-mode fiber (SMF) is demonstrated for the first time. Under the pump of a 1480 nm laser diode, typical random laser radiation is achieved with an obvious threshold behavior as a function of pump power. Thanks to the fiber Bragg grating (FBG)-based half-opened cavity design and the efficient gain from the pumped erbium-doped fiber, a low threshold power of 10 mW is achieved, which is approximately two orders lower in magnitude than that of previously reported conventional random fiber lasers amplified through distributed Raman effects. Dual-wavelength lasing operation is also achieved by using two FBGs with different reflection wavelengths to collaborate with the distributed Rayleigh output mirror.

An actively Q-switched erbium-doped fiber laser with a fiber-pigtailed nanosecond ceramic optical switch is experimentally investigated in this paper. Firstly, the ceramic optical switch was systematically characterized. Then, it was used to actively Q-switch an all-fiber erbium-doped fiber ring laser. Stable Q-switching laser pulses with a repetition rate from 2 kHz–40 kHz were achieved. The minimum pulse width was measured to be ~25 ns at 2 kHz when pumped at 150 mW, and the corresponding maximum peak power was ~2.9 W. Multi-peak pulses were observed at low repetition rates and the reasons for these were analyzed. This study shows that a nanosecond ceramic switch can be used as a good Q switch due to its low insertion loss, high on/off ratio, ultrafast response, and low electrical power consumption.

In this paper, we study noise-like pulse generation in a km-long fibre ring laser including a double-clad erbium–ytterbium fibre and passively mode-locked through nonlinear polarization evolution. Although single noise-like pulsing is only observed at moderate pump power, pulse energies as high as 120 nJ are reached in this regime. For higher pump power, the pulse splits into several noise-like pulses, which then rearrange into a stable and periodic pulse train. Harmonic mode locking from the 2nd to the 48th orders is readily obtained. At pump powers close to the damage threshold of the setup, much denser noise-like pulse trains are demonstrated, reaching harmonic orders beyond 1200 and repetition frequencies in excess of a quarter of a GHz. The mechanisms leading to noise-like pulse breaking and stable high-order harmonic mode locking are discussed.

The properties of amplified spontaneous emission (ASE) in CdSe/ZnS quantum dot (QD) doped step-index polymer optical fibers (POFs) were computationally analyzed in this paper. A theoretical model based on the rate equations between two main energy levels of CdSe/ZnS QD was built in terms of time (t), distance traveled by light (z) and wavelength (λ), which can describe the ASE successfully. Through analyzing the spectral evolution with distance of the pulses propagating along the CdSe/ZnS QD doped POFs, dependences of the ASE threshold and the slope efficiency on the numerical aperture were obtained. Compared to the ASE in common dye-doped POFs, the pump threshold was just about 1/1000, but the slope efficiency was much higher.

An approach that can be used to generate more complex and interesting optical fields is proposed by controlling the phase, position, size and amplitude of each coherent array. To illustrate the advantages of the approach, the power coupling efficiency of the optical systems with Cassegrain-telescope receivers is studied. It shows that the approach exhibits greater advantage over traditional coherent combining beams.

A novel configuration of a phase-sensitive optical time-domain reflectometer (OTDR) utilizing dual-pulse phase modulations of the probe signal is presented and experimentally demonstrated. The proposed modulation method enables one to perform the demodulation and reconstruction of an external perturbation signal which impacts the fiber using the phase diversity technique. The proposed phase-sensitive OTDR has some advantages in comparison with conventional solutions, which are discussed. The feasibility of a double pulse OTDR with phase modulation is demonstrated and theoretically proved.

An analytical power model based on the rate equations of a high-power Yb-doped double-clad fiber laser is presented. Although it considers combiner and splices losses for the first time, the maximum and mean relative errors are less than 2.2% and 3.04% when compared with numerical and experimental results, respectively. Furthermore, an analytical temperature model based on thermal conduction equation has been reported. For the first time, the radial-dependent distribution of the heat density generated inside the fiber core is considered. Radial and longitudinal 3D distributions for temperature are presented. The results show a big difference (can reach 25%) when compared with conventional models, which consider a uniform radial distribution for heat density. In contrast, the mean relative error related to our model is less than 4.7% when compared with experimental results, whereas it reaches 9.3% in the conventional one.

A stable multi-wavelength polarization-maintaining erbium-doped fiber (PM-EDF) laser with high signal-to-noise ratio (SNR) based on a compounded nonlinear polarization rotation effect (CNPRE) is proposed and demonstrated. In order to effectively reduce homogeneous broadening of EDF and then to the alleviate mode competition, two sandwich configurations formed by a polarization dependent isolator (PDI) or a segment of single-mode fiber sandwiched between two polarization controllers (PC), are introduced into the ring cavity to generate the CNPRE. A home-made asymmetry twin-core fiber (ATCF) is also incorporated in the ring cavity as a comb filter. With only 150 mW pump power, there are up to 45-wavelengths lasing with the approximate amplitude in a 3 dB bandwidth generated at room temperature. The wavelength spacing between the adjacent peaks is 0.29 nm and the highest SNRs reach 41.5 dB by optimizing the state of polarization of PCs. The power fluctuation and wavelength shift for each lasing wavelength are less than 0.05 dB and 0.02 nm, respectively. This indicates that the proposed multi-wavelength fiber laser can be stably operated at room temperature.

This work proposes a new method to enhance the performance of an S-band fiber laser by using a thulium-doped photonic crystal fiber (PCF). The proposed method is based on amplified spontaneous emission (ASE) suppression provided by the thulium-doped PCF unique geometric structure. The enhanced performance of this filter based PCF is dependent on the short and long cut-off wavelength characteristics that define the fiber transmission window. Realizing the short wavelength cut-off location requires the PCF cladding to be doped with a high index material, which provides a refractive index difference between the core and cladding region. Achieving the long cut-off wavelength necessitates enlarging the size of the air holes surrounding the rare-earth doped core region. The PCF structure is optimized so as to achieve the desired ASE suppression regions of below 0.8 μm and above 1.8 μm. The laser performance is simulated for different host media, namely pure silica, alumino-silicate, and fluoride-based fiber ZBLAN based on this thulium-doped PCF design. The host media spectroscopic details, including lifetime variations and quantum efficiency effect on the lasing emission are also discussed. Information on the filter based PCF design is gathered via a full-vectorial finite element method analysis and specifically a numerical modelling solution for the energy level rate equation using the Runge–Kutta method. Results are analyzed for gain improvement, lasing cavity, laser efficiency and effect of core size diameter variation. Results are compared with conventional thulium-doped fiber and thulium-doped PCF for every single host media. We observe that the ZBLAN host media is the most promising candidate due to its greater quantum efficiency.

A full quantum microscopic theory is developed to analyze a biexciton radiative cascade coupled to bulk acoustic phonons in a quantum dot. By considering the phonon sub-system in coherent state representation a new approach is proposed for investigating the phonon effects. Via this approach it is possible to obtain an exact analytical result for the phonon kernel in this system. This approach is introduced in the context of an example: the process of generating polarization-entangled photon pairs from the biexciton cascade in a quantum dot. We calculate the exact density matrix (using quantum state tomography) of photons and their concurrence. We show that the exchange interaction and temperature have remarkable effects on the degree of entanglement of the emitted photons. The approach introduced provides an exact analytical result for finite discrete electron states interacting with phonons.

A novel configuration is proposed to study optical bistability (OB) and optical multistability (OM) in a superconducting quantum circuit with a tunable V-type artificial molecule constructed by two superconducting Josephson charge qubits coupled with each other through a superconducting quantum interference device. We find that the ratio of the Josephson coupling energy to the capacitive coupling strength has a significant impact on creating optical bistability. The influence of other system parameters on bistable behavior of the artificial medium is then discussed. In particular, it is found that applying an incoherent pumping field can noticeably reduce the bistable threshold. We also realize a switch from OB to OM through proper tuning of detuning parameters. The controllability of OB and OM of this artificial molecule may be useful in building logic-gate devices for optical computing and quantum information processing and provide some new possibilities for solid-state quantum information science.

Time-bin entangled single-photons are highly demanded for long distance quantum communication. We propose a heralded source of tunable narrowband single photons entangled in well-separated multiple temporal modes (time bins) with controllable amplitudes. The detection of a single Stokes photon generated in a cold atomic ensemble via Raman scattering of a weak write pulse heralds the preparation of one spin excitation stored within the atomic medium. A train of read laser pulses deterministically converts the atomic excitation into a single anti-Stokes photon delocalized in multi-time-bins. The waveforms of bins are well-controlled by the read pulse parameters. A scheme to measure the phase coherence across all time bins is suggested.

A meaningful increase in the number of NIR emission centers was experimentally observed in bismuth-doped multicomponent silicate glasses additionally doped with germanium dioxide. The emission and excitation spectra of the glass sets were monitored and compared with the spectra of radiative oxygen-deficient centers in vitreous silica and germania.

We generalize the correct account for molecule vibrational motion in tunnelling ionization, proposed earlier (Kornev and Zon 2012 Phys. Rev. A 86 043401), to the case of polar molecules. We consider the tunnel effect in both dc and ac fields, taking into account perturbation of vibrational motion by an external field. We develop a method for accounting for dipole moment on the base of the electronic wave function expansion over dipole-spherical functions instead of ordinary spherical functions. The change of polar molecule ionization probability compared to non-polar molecule ionization is mainly due to constant change in the asymptotic form of the valence electron wave function, both in the dc and ac fields. We present numerical results for HF and HCl molecules of various isotopic proportions for specific orientations of the molecule axis relative to the electric field strength. The maximum rate of the tunnel effect for these molecules is achieved if the internuclear axis is oriented perpendicularly to the electric field.

We report a numerically designed highly nonlinear all-glass chalcogenide microstructured optical fiber (MOF) for the efficient generation of light around 6 µm through degenerate four-wave mixing by considering a continuous wave CO laser of 5–10 W power emitting at 5.6 µm as the pump. By tuning the pump wavelength, pump power, fiber dispersion and nonlinear properties, a narrow (N)- and/or broad (B)- band mid-IR all-fiber light source could be realized. Parametric amplification of more than 20 dB is achievable for the N-band source at 6.46 µm with a maximum power conversion efficiency (C_m) ~ 33%, while a amplification ~22  ±  2 dB is achievable for a B-band source over the wavelength range of 5–6.3 µm with a C_m > 40%.

The nonlinear dynamics of an Airy beam in a saturated medium is presented. An analytical expression for the evolution of the Airy beam width in the root-mean-square sense is derived. The novel features of the collapsing beams of an Airy beam in a saturated medium are demonstrated by numerical calculation. These collapsing beams shift laterally and are the main property of the Airy beam. However, the collapsing beam in the major lobe of an Airy beam tends to shift in the opposite direction for conservation of the beam centroid. The location and evolution of the collapsing beams depend strongly on the initial powers. The peak intensities of the collapsing beams oscillate at almost the same intensity in the saturated medium, regardless of their initial powers. These results are useful for manipulating nonlinear wave collapse and multi-filamentation.

This paper investigates how to obtain a wide and stable optical frequency comb in an intensity-modulated continuous-wave pumped optical fiber by straightforwardly characterizing the signal-to-noise ratio and analyzing the optimal fiber length. The stability of the obtained optical frequency comb is analyzed by a method which is similar to the eye pattern. The prospect for obtaining wider and more stable optical frequency combs is discussed.

We propose a four-level experimental N-type atomic configuration to observe the propagation of a light pulse in a spinning dispersive medium. In this model a fast propagating light pulse is observed in which the polarization states of the light and their transmitted images are rotated in the opposite direction to the spinning medium. We investigate the effects of Doppler broadening and Kerr nonlinearity on fast light propagation in a spinning medium. Doppler broadening and Kerr nonlinearity strongly influence the rotation of the polarization states of the light and images of fast light in a spinning medium. A pulse of group velocity −c/2000.5 ms⁻¹ is enhanced to −c/80000 ms⁻¹ due to the the Kerr effect and a significant increase is observed in the rotation of the polarization states of the light and images. At a specific parameter, a 25% fraction change is observed due to the Kerr effect. These results provide different rotation states for image coding.

Quasi-phase-matching (QPM) of the harmonics of ultrashort pulses in the perforated aluminum, indium, and chromium plasma plumes produced by different techniques is analyzed. We extend our recent studies (2014 J. Phys. B: At. Mol. Opt. Phys.47 105401) to other plasma ablations and show the advantages of modulated plasma profiles for the harmonic generation. We demonstrate the 20 × growth of QPM-enhanced harmonics in the plasma produced on the perforated aluminum surface. The calculations of plasma concentrations at different delays and distances from ablating targets are presented. We show the tuning of maximally enhanced harmonics using variable excitation of metallic targets at the conditions of QPM, as well as demonstrate the use of a two-color pump of the four-jet indium plasma for enhancement of the harmonics, which were not present in the spectra obtained from the extended indium plasma.

Properties of Bose–Einstein condensates (BEC) are studied in the presence of a Gaussian random potential of arbitrary strength of disorder and with arbitrary correlation length. Using the stochastic mean field approximation, a system having arbitrary strength of interactions is treated at finite temperature. A special case, in which we assume that the second moment of the random potential is Lorentzian, is treated in more detail at zero temperature. The total density of particles consists of condensate density, glassy density and normal density components. Our results are in agreement with those of Huang and Meng (HM). The system is stable below the critical value of the disorder parameter and undergoes a first-order phase transition at the critical value. We find that the critical value of the disorder parameter changes with changing the correlation length of the random potential.

We investigate the effects of vortex interaction on the formation of interference patterns in a coherent pair of two-dimensional Bose condensed clouds of ultra-cold atoms traveling in opposite directions subject to a harmonic trapping potential. We identify linear and nonlinear regimes in the dipole oscillations of the condensates according to the balance of internal and centre-of-mass energies of the clouds. Simulations of the collision of two clouds each containing a vortex with different winding number (charge) are carried out in these regimes in order to investigate the creation of varying interference patterns. The interaction between different vortex types can be clearly distinguished by those patterns.

We explain dynamical localization of Bose–Einstein condensate (BEC) in optomechanics both in position and in momentum space. The experimentally realizable optomechanical system is a Fabry–Pérot cavity with one moving end mirror driven by a single mode standing field. In our study we analyze variations in modulation strength and effective Planck's constant. Keeping in mind present day experimental advancements, we suggest parameteric values to observe the phenomenon in the laboratory.

We study quantum coherence of strongly interacting cold bosons in a double-well potential driven by a laser field. The system is initially in a Fock state and, either with or without a static tilting field, evolves into coherent states. The coherence is resonantly enhanced by photon-assisted tunneling. For the tilted wells, it reveals a two-branch pattern that corresponds to multiple photon absorption or emission.

The preoperative and intraoperative diagnosis of parotid gland tumors is difficult, but is important for their surgical management. In order to explore an intraoperative diagnostic method, Raman spectroscopy is applied to detect the normal parotid gland and tumors, including pleomorphic adenoma, Warthin's tumor and mucoepidermoid carcinoma. In the 600–1800 cm⁻¹ region of the Raman shift, there are numerous spectral differences between the parotid gland and tumors. Compared with Raman spectra of the normal parotid gland, the Raman spectra of parotid tumors show an increase of the peaks assigned to nucleic acids and proteins, but a decrease of the peaks related to lipids. Spectral differences also exist between the spectra of parotid tumors. Based on these differences, a remarkable classification and diagnosis of the parotid gland and tumors are carried out by support vector machine (SVM), with high accuracy (96.7~100%), sensitivity (93.3~100%) and specificity (96.7~100%). Raman spectroscopy combined with SVM has a great potential to aid the intraoperative diagnosis of parotid tumors and could provide an accurate and rapid diagnostic approach.

Colorectal cancer (CRC) is the third most common cancer and the third leading cause of cancer death worldwide. Recurrence is a major problem and is often the ultimate cause of death. In this context, the tumor microenvironment influences tumor progression and is considered as a new essential feature that clearly impacts on treatment outcome, and must therefore be taken into consideration. Photodynamic therapy (PDT), oxygen, light and drug-dependent, is a novel treatment modality when CRC patients are inoperable. Tumor vasculature and parenchyma cells are both potential targets of PDT damage modulating tumor–stroma interactions. In biological activity assessment in photodynamic research, three-dimensional (3D) cultures are essential to integrate biomechanical, biochemical, and biophysical properties that better predict the outcome of oxygen- and drug-dependent medical therapies. Therefore, the objective of this study was to investigate the antitumor effect of methyl 5-aminolevulinic acid-PDT using a light emitting diode for the treatment of CRC cells in a scenario that mimics targeted tissue complexity, providing a potential bridge for the gap between 2D cultures and animal models. Since photodynamic intervention of the tumor microenvironment can effectively modulate the tumor–stroma interaction, it was proposed to characterize the endothelial response to CRC paracrine communication, if one of these two populations is photosensitized. In conclusion, we demonstrated that the dialogue between endothelial and tumor populations when subjected to lethal PDT conditions induces an increase in angiogenic phenotype, and we think that it should be carefully considered for the development of PDT therapeutic protocols.

Two-photon excited fluorescence (TPEF) microscopy has become a powerful instrument for imaging unstained tissue samples in biomedical research. The purpose of this study was to determine whether TPEF imaging of histological sections without hematoxylin-eosin (H-E) stain can be used to characterize lesions and identify surgical margins in pancreatic metastasis from renal cell carcinoma (RCC). The specimens of a pancreatic metastasis from RCC, as well as a primary RCC from a patient, were examined by TPEF microscopy and compared with their corresponding H-E stained histopathological results. The results showed that high-resolution TPEF imaging of unstained histological sections of pancreatic metastasis from RCC can reveal that the typical morphology of the tissue and cells in cancer tissues is different from the normal pancreas. It also clearly presented histopathological features of the collagenous capsule, which is an important boundary symbol to identify normal and cancerous tissue and to instruct surgical operation. It indicated the feasibility of using TPEF microscopy to make an optical diagnosis of lesions and identify the surgical margins in pancreatic metastasis from RCC.

We report a novel scheme of an adaptive optical microphone (AOM) based on two-wave mixing in a photorefractive crystal. The sensitive element of the microphone is a thin metal membrane which receives acoustic waves and modulates a light phase that is demodulated by means of a dynamic hologram continuously recorded in a photorefractive CdTe crystal. Due to the interferometric operation principle, the AOM possesses an ultra-high sensitivity to acoustic pressure (4.3 rad Pa⁻¹ at a frequency of 1 kHz), low detection threshold (0.79 mPa or 32 dB) and large dynamic range (55 dB), while the adaptive properties of a dynamic hologram allow one to perform a measurement in an unstable environment.

Practical properties and physical characteristics of low intensity lasers have made possible their application to treat soft tissue diseases. Excitation of intracellular chromophores by red and infrared radiation at low energy fluences with increase of mitochondrial metabolism is the basis of the biostimulation effect but free radicals can be produced. DNA lesions induced by free radicals are repaired by the base excision repair pathway. In this work, we evaluate the expression of POLγ and APEX2 genes related to repair of mitochondrial and nuclear DNA, respectively. Skin and muscle tissue of Wistar rats were exposed to low intensity infrared laser at different fluences. One hour and 24 hours after laser exposure, tissue samples were withdrawn for total RNA extraction, cDNA synthesis, and evaluation of POLγ and APEX2 mRNA expression by real time quantitative polymerase chain reaction. Skin and muscle tissue of Wistar rats exposed to laser radiation show different expression of POLγ and APEX2 mRNA depending of the fluence and time after exposure. Our study suggests that a low intensity infrared laser affects expression of genes involved in repair of oxidative lesions in mitochondrial and nuclear DNA.

The present study is concerned with the in vitro study of different sized titanium dioxide (TiO₂) nanoparticles' (NPs) penetration and accumulation in human normal lung (NL) tissue and lung adenocarcinoma tumor (LAT) tissue by the methods of continuous optical coherence tomography (OCT) monitoring and diffuse reflectance (DR) spectra measurement, and their evaluating the effects of TiO₂ NPs in two sizes (60 nm and 100 nm) and their combination with ultrasound (US) on the optical properties of human NL and LAT tissue. Spectral measurements indicate that TiO₂ NPs penetrate and accumulate into the tissues and thus induce enhancement of DR. The averaged and normalized OCT signal intensity suggests that light penetration depth is significantly enlarged by ultrasound. The average attenuation coefficient of NL tissue changes from 5.10  ±  0.26 mm⁻¹ to 3.12  ±  0.43 mm⁻¹ and 2.15  ±  0.54 mm⁻¹ at 120 min for 60 nm TiO₂ NPs and 60 nm TiO₂NPs/US treatment, respectively, and from 5.54  ±  0.46 mm⁻¹ to 3.24  ±  0.73 mm⁻¹ and 2.69  ±  0.34 mm⁻¹ at 150 min for 100 nm TiO₂ NPs and 100 nm TiO₂NPs/US, respectively. The average attenuation coefficient of LAT tissue changes from 9.12  ±  0.54 mm⁻¹ to 4.54  ±  0.39 mm⁻¹ and 3.61  ±  0.38 mm⁻¹ at 120 min for 60 nm TiO₂ NPs and 60 nm TiO₂NPs/US treatment, respectively, and from 9.79  ±  0.32 mm⁻¹ to 5.12  ±  0.47 mm⁻¹ and 4.89  ±  0.59 mm⁻¹ at 150 min for 100 nm TiO₂ NPs and 100 nm TiO₂NPs/US, respectively. The results suggest that the optical properties of NL and LAT tissues are greatly influenced by TiO₂ NPs and their combination with ultrasound.

Immune reactions play an important role in determining the biostimulation of bone formation, either in new bone formation or inflammatory fibrous tissue encapsulation. Macrophage cell, the important effector cells in the immune reaction, which are indispensable for osteogenesis and their heterogeneity and plasticity, render macrophages a primer target for immune system modulation. However, there are very few studies about the effects of macrophage cells on laser treatment-regulated osteogenesis. In this study, we used CO₂ laser as a model biostimulation to investigate the role of macrophage cells on the CO₂ laser stimulated osteogenesis. Bone morphogenetic protein 2 (BMP2) was also significantly up regulated by the CO₂ laser stimulation, indicating that macrophage may participate in the CO₂ laser stimulated osteogenesis. Interestingly, when laser treatment macrophage-conditioned medium were applied to human periodontal ligament cells (hPDLs), the osteogenesis differentiation of hPDLs was significantly enhanced, indicating the important role of macrophages in CO₂ laser-induced osteogenesis. These findings provided valuable insights into the mechanism of CO₂ laser-stimulated osteogenic differentiation, and a strategy to optimize the evaluation system for the in vitro osteogenesis capacity of laser treatment.

Using the exact analytical expressions for the reflection and transmission matrices for the finite thickness cholesteric liquid crystal (CLC) layer, we calculated its photonic density of states (PDS) of the eigen polarizations (EPs). We investigated the influence of absorption and gain, as well as the CLC cell thickness and CLC local dielectric anisotropy on PDS. We presented the full picture of distribution of total field in the CLC layer and outside it for two EPs. The possibility of connections between the PDS and the density of the light energy accumulated in the medium was investigated, and it was shown that these characteristics had analogous spectra and, besides, the influences of the problem parameters on these characteristics were also analogous. We showed that there existed a critical value of the parameter characterizing the gain beyond which the lasing mode was quenched and the feedback vanished. We showed that in the presence of gain there existed a critical value of numbers of pitches in the CLC layer beyond which the lasing mode was again quenched and the feedback vanished, too. It is shown that the subject system can work as a low-threshold laser or a multi-position trigger.

The present paper considers two gain GRIN media, characterized by a complex parabolic and hyperbolic secant refractive index profile, for the design of uniform beam shaper systems. A general condition for beam shaping is obtained from the equation describing the evolution of the half-width of a plane Gaussian beam in the GRIN media. The simulation of the irradiance evolution of an input plane Gaussian beam—operating at 575 nm and beam waist radius of 0.45 mm—in each material is shown, in order to examine the beam shaping quality in terms of thickness of the active GRIN media and input beam wavelength.

In this paper, we demonstrated multimode laser emission from a dome shaped micro-scale resonator encapsulated in a flexible polymer film. The resonator with a radius of ~60 microns was made of Norland Blocking Adhesive (NBA 107) doped with a solution of rhodamine 6G and ethanol. The dome was encapsulated in a flexible polymeric film made of polydymethylsiloxane (PDMS) with a thickness of 1 mm. The micro-scale laser was optically pumped using a frequency doubled Q-switch Nd:YAG laser with pulse repetition of 10 Hz and pulse duration of 9 ns. Experiments were carried out to investigate the lasing properties of this laser structure. The pumping threshold for multimode laser emission was below 100 µJ cm⁻². The average optical quality factor for all observed laser modes was of the order of 10⁴. Using a fluence of 315.8 µJ cm⁻² it was observed that the intensity of the laser emission dropped by 62% after 5 min of operation. These results showed that these solid state flexible lasers are easy to fabricate and can be integrated into novel flexible photonic devices and novel photonic sensors.

This study investigates changes in ablation efficiency and surface morphology induced in human dental enamel and dentin upon interaction with femtosecond laser pulses at variable energies and number of laser pulses. Craters were created using a Ti:sapphire femtosecond laser ablation system operating at a wavelength of 785 nm, pulse width of 130 fs, and repetition rate of 20 Hz. Various techniques, such as optical and scanning electron microscopy and inductively coupled plasma mass spectrometry (ICP-MS), were used to evaluate ablation depth, amount of material ablated, and surface morphology of the craters. Ablation rate (ablation depth per pulse) was found to be lower in enamel than dentin with the maximum rate occurring at fluence of 12.4 J cm⁻² in both materials. A drop in ablation rate was observed for fluence greater than 12.4 J cm⁻² and was attributed to attenuation of laser energy due to interaction with the laser-generated particles. Above this fluence, signs of thermal effects, such as melting and formation of droplets of molten material at the sample surface, were observed. The response of the ICP-MS indicated that the amount of ablated material removed from dentin is greater than that removed from enamel by a factor of 1.5 or more at all investigated fluence.

New experimental data on the secondary electron yield from a thin layer of ⁵⁷Fe irradiated by emission of the hot dense plasma source created by femtosecond laser pulses with intensity of 10¹⁷ W cm⁻² is presented. Plasma source hard x-ray and electron fluxes are measured for the source characterization. Thorough statistical analysis of the delayed secondary electron spectrum from the ⁵⁷Fe layer in the 20–100 ns temporal window allows exclusion of the 'null' hypothesis of the random character of the differences of this spectrum with that obtained using a ⁵⁶Fe target. Thus, statistically valid maxima at ∼5.8 and 7.4 keV can be attributed to the decay of the isomeric nuclear state of ⁵⁷Fe (3/2⁻, 14.41 keV, 98 ns) by the internal conversion process through the atomic K-shell (maximum at 7.4 keV), followed by the Auger process (maximum at 5.8 keV).