This PDF file contains the front matter associated with SPIE Proceedings Volume 7994, including the Title Page, Copyright information, Table of Contents, Introduction (if any) and the Conference Committee listing

Radiation characteristics of planar diffusion-cooled CO₂- and CO-lasers created using the same design and excited by a RF discharge at a frequency of 40 MHz have been studied. A single-mode cw lasing power of ~ 100 W has been achieved with an efficiency of ~ 10 % for a CO₂-laser with a diffraction-limited radiation divergence of 4 - 7 mrad. For a CO-laser with electrode temperature of -65 °C, a cw output power of 60 W with an efficiency of ~ 10% has been achieved in the wavelength range 5.3 - 6.0 μm.

Development of KrF laser system for lidar designed for detection of the compound molecules containing a nitric oxide is presented. The system consists of the master oscillator and the amplifier operating at pulse repetition rate up to 100 Hz. Laser radiation having energy up to 0.2 J and bandwidth of 2 pm is smoothly tuned in a spectral range of 247.6-249.5 nm.

A new lasing mechanism for semiconductors like CuCl, CuBr is proposed based on the two-photon pumping of biexcitons from the ground state of the crystal and generation or amplification of light in the region of M-band of luminescence due to the optical exciton-biexciton conversion. It was shown that the net gain essentially depends on the level of two-photon pumping and rapidly decreases deep into the crystal due to the spatial depletion of pump radiation. Estimations for CuCl give the values of lasing photons with the energy about 3,2 eV and the maximum small signal gain about the value of the exciton absorption coefficient.

Passively mode-locked bidirectional operation of a ring diode pumped Nd:YVO₄ laser with optimized resonator design is reported. Beat note with frequency between 140 Hz and 300 Hz between two counter propagating beams was observed and its origin is explained as a result of phase modulation of the laser beam via nonlinear index of refraction n₂ of Nd:YVO₄ which was calculated.

We report on the microjoule pulse energy achieved in mode-locked erbium fiber lasers with kilometers-long normaldispersion cavities. We also show that generated highly-chirped pulses are subject to efficient compression when propagating in anomalous-dispersion telecom fibers.

The statistical characteristics of spatial fluctuations of the intensity of dispersed laser beams are studied theoretically. The density of the probability distribution for the intensity is found and its transformation with a change in the longitudinal coordinate is studied. It is shown that a decrease in the intensity fluctuations and a drop in the contrast of the beam speckle structure occur with increasing distance from the initial plane in which the spatially inhomogeneous broadband field is assumed to be spatially coherent. A decrease in fluctuations is accompanied by an increase in the size of speckles in the direction of dispersion, as well as along the beam axis. An interpretation of the found regularities is given.

A theoretical study is made of geometry average statistical speckles of the intensity of a broadband dispersed laser beam which is spatially coherent in the initial plane z = 0. Two-dimensional distributions of random intensity are numerically simulated, which make it possible to trace transformation of speckle patterns in the course of the beam propagation. The correlation functions and power spectra of random intensity are calculated to show how the characteristic dimensions and the shape of speckles vary depending on longitudinal coordinate z, the width and shape of the frequency spectrum and also the degree of dispersion of the light beam. Analytical expressions are derived which show that the speckle dimensions increase in the longitudinal direction as well as in the direction of the dispersion as the distance from the initial plane increases. Limit value (at z → ∞ ) of the speckle width in the direction of the beam dispersion is calculated.

The spatial characteristics of the focused beam of a fiber 2 kW laser have been measured. The problems of matching this beam structure, greatly differing from the Gaussian form, with technological operations have been considered.

The results of theoretical and experimental study of thermal lensing in diode-pumped Yb:YVO₄ laser crystal, Yb:Y₂O₃ and Yb:Sc₂O₃ laser ceramics are presented. Shown, that influence of thermo-lensing effect is necessary to consider for creation of effective high-intensity femtosecond Yb-doped laser systems.

Thermally induced beam distortions in laser ceramics with arbitrary grain size have been investigated. A model for the spatial spectral density of dielectric permeability variations was suggested. The average scattered intensity was carried out using the small disturbances method. The directional pattern of the scattered field and the extinction coefficient have been obtained. The scattered power and the depolarization ratio fit with the corresponding values obtained in the geometrical optics approximation in the range of its validity.

Experimental and theoretical modeling results for pulsed diode-array end-pumped Nd:YAG laser with aberrational thermolens are presented. Millijoule level energy stable picosecond pulse generation is realized in a wide range of repetition rates. Limiting factors of stable laser operation and quantitative contribution of aberrations in beam quality degradation are discussed.

By using a bulk GaAs as an output coupler as well as a saturable absorber, with changing of concentration of defects inside the laser cavity, Q-switching of flash-lamp pumped Nd:YAG laser has been studied. It is shown that the mechanism of formation of the laser pulses, in a wide range of duration which were reported in a lot of previous papers is caused by the intracavity changes of the defect concentration in a GaAs.

Photophysical and lasing properties of the well known PM567, PM580 and PM697 and three new dipyrromethene derivatives are presented. The laser efficiency and spectrum characteristics were investigated as functions of dye concentration and pumping intensity in ethanol solutions under second harmonic of Nd-YAG-laser. Laser characteristics and photostability for PM567 are presented also in the solid state matrixes (P(MMA=13%POSS), PMMA).

In present work the results of measurements of segregation coefficient of Nd³⁺ ions in LiLu_xY_1-xF₄ (x=0- 1) crystals are presented. Two methods for Nd³⁺ ions concentration measurements in the crystals are used. The first one - X-ray fluorescence analysis (XRFA) - is used to establish the absolute concentration of impurity ions, and the second - optical absorption spectroscopy (OAS) - allows to estimate not absolute, but relative impurity concentration. By comparison of the results given by both methods the integral cross-sections of ⁴I_9/2-²G_7/2 transitions of Nd³⁺ ions doped in these crystals were estimated. Thus, the standard samples, allowing to establish the absolute Nd³⁺ ions concentration in LiLu_xY _1-x F₄(x=0- 1) crystals by means of OAS-method, were created.

Here we report on pump-probe studies of KY₃F₁₀ and CaF₂ doped with Ce³⁺ and Yb³⁺ ions. The crystals Ce³⁺:KY₃F₁₀ and Ce³⁺:CaF₂ show attractive spectral characteristics for tunable UV lasers application but have poor photochemical stability. Their properties under intense UV pumping are affected by excited state absorption and color centers formation. This work was aimed at dynamic processes investigation induced by laser radiation of UV spectral range in KY₃F₁₀ and CaF₂ doped with Ce³⁺ and Yb³⁺ ions. Optical gain was observed on CaF₂:³⁺+Yb³⁺ in the range 325-335 nm for the first time. It proves Yb³⁺ ions coactivation antisolarant effect elaborated by us earlier. It is shown that in investigated crystals under a pump radiation, resonant to 4f-5d Ce³⁺ ions transitions several types of color centers (CC) are formed. Set of these CC types are determine the absorption at expected stimulated emission spectral range and magnitude of the induced loses is dependent on many factors. As a result of competition between CC formation, free charges recombination and CC photodestruction this balance can be shifted towards either rising or dropping losses at 5d-4f Ce³⁺ ions luminescence spectral range.

Here laser studies of Ce³⁺:LiLu_xMe_1-x F₄ (Me=Y³⁺,Yb³⁺) mixed crystals homologous to well-known Ce³⁺:LiYF₄and Ce³⁺:LiLuF₄ UV crystalline active media are reported. Optical spectroscopy and X-ray diffraction studies have proved scheelite structure of the investigated mixture crystals. Advantages of LiLuYF₄:Ce³⁺+Yb³⁺ mixture crystals were detected. Among them an opportunity to wider tuning range of laser oscillation in comparison to LiLuF₄:Ce³⁺+Yb³⁺ active medium by means of varying YF₃/LuF₃ content relation. As it was shown from laser experiments mutual shift of 5d-4f emitting transition of Ce³⁺ ions and color centers absorption band due to lattice parameter change gives an optimum for YF₃/LuF₃ content relation corresponding to minimal overlap and maximal amplification band. EPR and optical spectroscopy revealed the optimum ratio of Y³⁺ ions and Lu³⁺ in solid solutions of LiF-LuF₃-YF₃, where the segregation coefficient Ce³⁺ of ions is increased 3-5 times compared with crystals LiYF₄ and LiLuF₄.

We have discovered that total intracavity losses, being dependent on color centers amount, go down for higher pump energies for LiCaAlF₆: Ce³⁺. This dependence is explained by the formation by the pump radiation and destruction of color centers due to laser radiation. The more energy remains in the lasing cavity, the lower the color centers absorption. Such dependencies were investigated for active medium crystals grown by different methods. Influence of growth conditions on active media characteristics is discussed. As a result we have shown for the first time that the crystal LiCaAlF₆:Ce³⁺ internal losses depend on the pump energy. Method has been worked out to determine the intracavity losses of the laser, which allows evaluation of prospects of its practical use in the most correct way.

Light scattering patterns have been calculated for a simple optical model constructed for single smooth and nonsmooth lymphocytes of healthy and infected individuals. It has been shown that the smooth and nonsmooth cells can be resolved using the intensities of the sideward and backward scattered light. We have found by calculations and validated by the flow-cytometer experiments that intensity distributions for the cells of lymphocyte populations can be used as a preliminary signatures of some virus infections. Potential biomedical applications of the findings for label-free flowcytometry detecting of individuals infected with viruses of hepatitises B or C and some others viruses are presented.

In a frequency-modulation spectroscopy experiment, using the radiation from a single frequency diode laser, the spectra of molecular iodine hyperfine structure near 640 nm were recorded on the transition B³Π⁺_0u- X¹Σ⁺_g . The frequency reference given by the value of the modulation frequency (12.5 MHz in given experiment) allows determination of the frequency differences between hyperfine components with accuracy better than 0.1 MHz using the fitting procedure in experiment with only one laser.

The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of semiconductors and dielectrics by linearly polarized high-intensity Ti:sapphire fs-laser pulses (τ ~100 fs, λ ~800 nm) is studied experimentally and theoretically. In the experiments, two different types of LIPSS exhibiting very different spatial periods are observed (socalled LSFL - low spatial frequency LIPSS, and HSFL - high spatial frequency LIPSS), both having a different dependence on the incident laser fluence and pulse number per spot. The experimental results are analyzed by means of a new theoretical approach, which combines the generally accepted LIPSS theory of J. E. Sipe and co-workers [Phys. Rev. B 27, 1141-1154 (1983)] with a Drude model, in order to account for transient changes of the optical properties of the irradiated materials. The joint Sipe-Drude model is capable of explaining numerous aspects of fs-LIPSS formation, i.e., the orientation of the LIPSS, their fluence dependence as well as their spatial periods. The latter aspect is specifically demonstrated for silicon crystals, which show experimental LSFL periods Λ somewhat smaller than λ. This behaviour is caused by the excitation of surface plasmon polaritons, SPP, (once the initially semiconducting material turns to a metallic state upon formation of a dense free-electron-plasma in the material) and the subsequent interference between its electrical fields with that of the incident laser beam, resulting in a spatially modulated energy deposition at the surface. Upon multi-pulse irradiation, a feedback mechanism, caused by the redshift of the resonance in a grating-assisted SPP excitation, is further reducing the LSFL spatial periods. The SPP-based mechanism of LSFL successfully explains the remarkably large range of LSFL periods between ~0.6 λ and λ.

Formation of stable micro-protrusions and microstructures ("microtowers") on surface of liquid metals during multipulse irradiation by UV and IR lasers in different ambient gases was discovered. The rates of the structure formation have been measured which can reach 5 - 20 μm/pulse depending on the metal and ambient gas sort. Single micro-protrusions 1-2 mm in length were formed with diameter approximately two times greater than the focal spot size. The possibility to control the microstructure shape is shown and their potential applications are demonstrated.

We combine in this work the measurement of local optical transmission in the near-field with the mapping of the third harmonic generation of semiconducting polymer samples. The use of a linear method with the scanning near-field optical microscope (SNOM) and a nonlinear method with the Third Harmonique Generation (THG) microscope reveal the variation and the nature of the nanomorphology of doped polyaniline thin films.

The dynamic of SH spectra modifications during channel formation in a solid target by high-intensity fs-laser radiation (I ~ 10¹⁶ W/cm²) has been investigated. A significant broadening and blue shift of the spectra were found.

We present a model suggesting high chemical activity of electronically-excited molecules colliding with an isolator surface. Initial photochemical event is accounted for as the result of molecular evolution on the electronically-excited potential energy surface (PES), where acceleration and alignment are taking place, guiding all the molecules towards the intersections with the ground state PES, where transitions to the ground state PES will occur with minimum energy dissipation. The accumulated kinetic energy may be used to overcome the chemical reaction barrier. While recombination chemical reactions in a gas phase require participation of a third body, this strong limitation on the reaction rates is removed upon interaction with a surface. To observe the predicted phenomenon, we suggested a new experimental approach, Evanescent Wave Photocatalysis1, based on application of total internal reflection on an insulator surface. Laser photoexcitation is localized in a narrow boundary gas layer just above the interface; majority of the excited molecules can reach the surface before the relaxation. The experiments are performed at high gas pressures, so that dense fluxes of the excited reagents can be readily produced. Products of chemical adsorption and/or chemical reactions induced within adsorbates are aggregated on the surface and observed by light scattering. We will demonstrate how pressure and spectral dependencies of the chemical outcomes, polarization of the light and interference of two laser beams inducing the reaction can be used to distinguish the new process we try to investigate from chemical reactions induced by photoexcitation within adsorbed molecules and/or gas phase photolysis.

The analysis of the possibilities of microstructuring (micromachining) of various solids by sharply focused femtosecond laser (fsl) capable of providing for a high intensity for moderate pulse energies remains quite topical. Usually the process takes place immediately at the focal spot and an extended structure can only be formed by scanning the sample. In our experiments focusing fsl pulses into a vacuum setup we produced extended microstructures (microdamages) on a few tens nm thickness gold foil deposited onto a fused-quartz substrate. The structure length has been an order of magnitude larger than the typical size of the irradiated region. The detection of Au⁺ photoions ensured a highly-sensitivite on-line diagnostics of this phenomenon and in the limit can be used for the probing of the picostructuring of solids irradiated by a laser. In the next step we are "cloning" the microstructure (microdamage) from one surface to another when there is a few tens microns vacuum-spacing between them and only one surface with a metal film is "directly" irradiated by fsl pulses. For the expertiment we prepared two similar fused-quartz prisms and pressed one sample to another. The clearance is determined by the thickness of a spacer (Cu-foil). The possible explanations are given.

Microstructure of defects in organic solar cells containing PEDOT:PSS:Sorbitol layer has been studied and conditions for successful pulsed laser annealing of them have been determined. Investigation with oblique illumination showed that radial symmetry of fine structure is an intrinsic property of either separated discotic defects or block structure. Our study shows that pulsed laser annealing of organic thin films in inert atmosphere has promising future.

The Mg_0.27Zn_0.73O/ZnO multiple quantum wells with different well width Lw have been grown by pulsed laser deposition method. The interface roughness of quantum wells was inherited from the bottom one and did not exceed 1 nm. The quantum confinement effect has been observed. The exciton binding energy of the two-dimensional Mg_0.27Zn_0.73O/ZnO structures was two times higher in comparison with the bulk ZnO. A sharp increase of exciton peak intensity in the photoluminescence spectra at well width reduction was observed. The optical excited stimulated emission in quantum wells Mg _0.27Zn_0.73O/ZnO with an excitation threshold ~210 kW/cm² has been demonstrated.

The processes of heat transfer in microparticles in the gas atmosphere due to kinetics of phase change (melting) under laser radiation have been numerically investigated. The temperature dependence of thermal and optical parameters, irradiative cooling and heat exchange with the gas atmosphere are considered. The dynamics of temperature distribution of particles of different sizes subject to melting has been determined. The dependences of the time of full melting on the properties of particles and on laser radiation have been obtained. This will help to choose the right regime of laser treatment in selective laser sintering.

The formation of laser-induced structures on the multicrystalline silicon surface has been investigated. Optimum performances of the surface structurization have been explored. A cardinal decrease in reflectance from modified surface has been discovered in a wide spectral range in comparison with the samples of chemically texturized monocrystalline silicon. The influence of subsequent chemical etching on the reflection spectra of the texturized samples surface has been analyzed.

Treatments by femtosecond Ti-sapphire laser (wavelength is 800 nm, pulse duration is <30 fs) and nanosecond KrF excimer laser (wavelength is 248 nm, pulse duration is 25 ns) were performed to study the impact of laser fluence, pulse duration and energy of photons on the process of chemical and structural reconstructions in GeO_x and GeO₂:Ge heterolayers. The solid GeO_x films are metastable and decompose into two phases - Ge and GeO₂. Nanosecond KrF laser irradiation produces significant shrinkage of GeO_x films and GeO₂:Ge heterolayers caped by thin SiN_xO_y or SiO₂ films. Pulse annealing by both types of lasers stimulate as the process of nanoclusters forming and crystallization of initial amorphous Ge-nanoclusters in the GeO₂ matrix. The possibility to use the solid germanium monoxide (GeO(s)) and GeO₂:Ge heterolayers (without cap layers) as nano-resist in laser nanolithography was demonstrated. The new nanostructured material was formed - the layers of nanofoam GeO₂ which can be obtained only with application of femtosecond laser pulse treatments.

A method to retrieve radius from 0.6 mkm up to 13.6 mkm and relative refractive index from 1.015 up to 1.28 of spherical homogeneous non-absorbing particles by multi-angle scattering is proposed. It is based on the formation of noise resistant functionals of the scattered intensity, which are invariant relatively linear homogeneous transformations of an intensity-based signal, and on the approximation of the retrieved parameters dependence on the functionals by a feed forward neural network. The values of intensity of light scattered in the interval of angles 10° - 60° are used. At 20% measurement errors the mean errors of the retrieval of radius and relative refractive index are 0.8% and 7%, respectively.

Filamentation of femtosecond laser pulses and self-writtten filament-induced waveguides were first among chalcogenide glassy semiconductors observed in glassy arsenic-germanium-sulfide. Recovery of refraction index profile of the self-written waveguide was carried out by solving transport of intensity equation and Abel inversion, using its ordinary microscopic images taken at different defocusing.

We realized a logical function of bit-to-bit parallel multiplication for optical echo-processor based on the third-order nonlinear optical response of a resonant medium at room temperature. As an operating medium we used the polyvinilbutural film doped with phthalocyanine dye. The result of the logical operation is presented in the spectrum of the nonlinear optical response after action of the two spectrally coded pumping pulses. The time of the logical operation is about 500 fs. We obtained the values of a homogeneous broadening of S₀ - S₁ line: Γ_hom = 89 cm^-1 at T = 300 K and Γ_hom = 44 cm^-1 at T = 77 K. The laser excitation parameters needed for effective operating of optical processor are defined. The maximum word length achievable under current experimental conditions is estimated.

Peculiarities of WO_x films fabrication by reactive pulsed laser deposition for high temperature Pt-oxide-SiC devices formation were investigated. Deposition of the oxide film was also carried out in such a way as to prevent deposition of droplet fraction (deposition with anti-droplet screen). Direct Simulation Monte Carlo and Kinetic Monte Carlo methods were performed for the deposition processes modeling. The response of the SiC-based devices to hydrogen-containing gases depends on the conditions of deposition of the oxide layer. The best properties were found in the sensor obtained by depositing the scattered flux of W atoms in a shady area on SiC substrate at an oxygen pressure of 10 Pa.

A relatively simple technique of high-energy ion implantation of the pulsed laser plasma under the influence of an external pulsed electric field is suggested. The developed mathematical model allows forecasting depth distribution of implanted atoms on the basis of experimental measurements of fundamental physical characteristics of the pulsed laser plasma and the technical parameters of high-voltage system. The possibility of implantation of platinum ions from laser plasma to create on-chip n-SiC hydrogen sensor for use in complicated conditions is demonstrated.

A remote study of a bubble wake in the sea by optical methods was carried out. Evolutions of the laser radiation Mie and Raman backscattering in a near-surface layer under cavitational perturbation induced by a passage of the high-speed boat provided lifetime estimate and dynamics of the bubble wake. Time evolution of the elastic scattering signal decayed completely after 0.5 minutes, while the RS signal exhibited longer life time. A calculated estimate for RS signal attenuation was 120 minutes, which is much longer then results obtained by acoustic methods.

Possibility to apply wide range CO-laser for detection of trace gas pollutions in multicomponent gas mixture is studied both theoretically and experimentally. Parameters of sensitivity and selectivity for multicomponent gas analysis with CO-laser were calculated.

A method of automated early fire detection based on the light detection and ranging (lidar) technology is presented. Specific lidar configurations and their application to forest and industrial-environment fire surveillance are discussed.

A low cost modular system for automatic oil spill detection, based on laser induced fluorescence light detection and ranging (LIF LIDAR) technology, which may be installed aboard watercraft and used for intensive surveillance of harborages, rivers, channels, and coastal waters, is described. First experimental results obtained with the developed LIF LIDAR detector prototype in the laboratory conditions are reported.

Chemical sensors and indicators based on different light guides (fiber- and integrated-optics) have been designed and tested, the sensitive substances having been introduced into outer layers of the light guides. The sensors are intended for detection of the solvent vapours such as acetone, ethanol, methanol etc. Obtained results and practical recommendations are discussed.

Vibration measurements of high-voltage insulators (bushings) of Moscow "Yuzhnaya" electric distribution substation have been performed by CW Doppler lidar based on 1.5 μm fiber laser with 1 W output. We observed sonic frequency vibrations of bushings in the range from ~ 1μm to several mm at the distances up to 40 m. Future development of the technique is discussed.

In the present work, the influence of the terahertz laser radiation at the frequencies of 1,15 and 3,68 THz on protein was studied. An increase in the optical density of irradiated samples on their absorption bands was revealed with the help of UV spectroscopy. This is an evidence of conformational changes in the protein molecule.

The results of research on repetitively-pulsed action of the laser plasma formed by subnanosecond pulses of the Ndlaser on hard tooth tissues (enamel, dentine) are given. Efficiency of designed laser-plasma technology is shown in comparison with conventional and laser methods.

In the recent decade the applications of photodynamic therapy (PDT) rapidly increase in several topics and one of areas where the PDT in the future will be play significant role is dentistry. The different photosensitizing complexes with a good water solubility and with absorption with an intensive maximum in the red region (630-690 nm), which makes them suitable for photodynamic treatments, were investigated. The photochemical properties of complexes for singlet oxygen generation were investigated and were shown relations between uptake levels and light intensity to achieve increase in photodynamic efficacy. Photodynamic efficacy against fungi Candida albicans and bacteria's E. faecalis, MRSA and S. Mutans in planktonic media was evaluated. The high photodynamic efficacy was shown for SiPc at very low concentrations (0.9 μM) and light doses of 50 J cm^-2 by intensity of light 60 mW cm^-2. The photodynamic response for E. faecalis, MRSA and S. Mutans, after treatments with different photosensitizers show strong dependence on concentrations of photsensitzers and micro organisms. The level of inactivation of the pathogen bacteria's from 1-2 degree of initial concentration up to full inactivation was observed. The studied complexes were compared to the recently studied Methylene blue, Haematoporphyrine and tetra-methylpirydiloxy Zn(II)- phthalocyanines and experimental results show that some of them have a good potential for inactivation of representative pathogenic bacterial strains. Experimental results also indicate that photodynamic therapy appears an effective method for inactivation of oral pathogenic bacterias and fungi.

Positively charged luminescent silica nanoparticles loaded with Tb(III) complex were prepaired by reverse microemulsion procedure with further modification by gemini surfactant. The ξ-potential values and dynamic light scattering data indicate high positive charge and colloidal stability of the as prepaired nanoparticles. The high affinity of these nanoparticles to anions is verified by spectrophotometric measurements with dye molecules, namely phenol red. The insertion of phenol red anions into surfactant bilayer at silica/water interface results in the quenching effect on Tb(III)-centered luminescence of the nanoparticles. Thus "on-off" switching of Tb-centered luminescence indicates the formation of the positively charged bilayer at the silica/water interface. The binding of dodecylsulfate anions with cationic adlayer at the silica/water interface results in the recharging of silica nanoparticles. This recharging can be manifested through the "off-on" luminescent switching, resulted from the displacement of dye anions and reestablishment of Tb(III)-centered luminescence.

The pathways of excitation energy transfer (EET) via pigments of the light-harvesting antenna are still in discussion. The bacteriochlorophyll fluorescence of peripheral light-harvesting complexes (LH2) from purple bacteria can be observed upon two-photon excitation (TPE) within 1200-1500 nm spectral range (a broad band near 1300 nm). Earlier the occurrence of this band was taken as an evidence for the participation of "dark" carotenoid S₁ state in EET processes (see [Walla et al., Proc. Nat. Acad. Sci. U.S.A. 97, 10808-10813 (2000)] and references in it). However we showed that TPE spectrum of LH2 fluorescence within 1200-1500 nm is not associated with carotenoids [Stepanenko et al., J. Phys. Chem. B. 113(34), 11720-11723 (2009)]. Here we present TPE spectra of fluorescence for chromatophores and lightharvesting complexes LH2 and LH1 from wild-type cells and from carotenoid-depleted or carotenoidless mutant cells of several purple bacteria. The broad band within 1300-1400 nm was found for all preparations. Absorption pump-probe femtosecond spectroscopy applied to LH2 complex from Rb. sphaeroides revealed the similar spectral and kinetic patterns for TPE at 1350 nm and one-photon excitation at 675 nm. Analysis of pigment composition of this complex by high-pressure liquid chromatography showed that even under mild isolation conditions some bacteriochlorophyll molecules were oxidized to 3-acetyl-chlorophyll molecules having the long-wavelength absorption peak in the 650-700 nm range. It is proposed that these 3-acetyl-chlorophyll molecules are responsible for the broad band in TPE spectra within the 1200-1500 nm region.

This work describes the progress in the developing of a hydrophonic sensors array, based on fiber laser technology, tailored for underwater acoustic surveillance of harbors, naval forces, and, in general, of maritime areas of strategic relevance; the same apparatus can also find application for marine mammals coastline surveying, simply addressing a suitable frequency detection band. The sensors are Distributed Bragg Reflectors Fiber Lasers. The laser active medium is an Er⁺ doped fiber included between two Bragg mirrors that are photo-imprinted through UV radiation on the fiber. The acoustic water pressure variations produce a longitudinal strain on the fiber laser structure with a consequent modulation of the emission wavelength. An in-fiber un-balanced Michelson interferometer transforms the wavelength modulation into phase modulation, enhancing the detection sensitivity. An acousto-optic modulator, mounted on one arm of the interferometer, generates a frequency carrier to allow conventional demodulation techniques. This apparatus has demonstrated a noise-equivalent level of less than 1 mPa/(Hz)^1/2 in the 0.5-5 kHz frequency band. Experimentations in marine environment of sensor arrays are in progress, and the first results obtained on a couple of sensors written on a same fiber are presented.

This report presents a review of recent developments in the investigation of propagation, excitation, and interaction of cladding modes in optical fibers used for sensing. The use of fiber cladding modes broadens the range of possible applications of fiber optical sensors. The cladding mode resonance excited by fiber Bragg gratings, in particular tilted Bragg gratings, is discussed. The most commonly used method of excitation of cladding modes based on long-period fiber gratings is considered. We describe applications of long-period fiber gratings as sensors of strain, temperature, refractive index, chemical composition, twist, etc. Propagation of cladding modes in fiber interferometers and cascaded long-period fiber gratings is analyzed.

Principal component analysis of UV-VIS-NIR transmission spectra of matured wine distillates (1-40 years aged) produced by three Moldavian manufacturers allows to characterize with sufficient certainty the eleven chemical parameters of considered alcoholic beverages: contents of acetaldehyde, ethyl acetate, furfural, vanillin, syringic aldehyde and acid, etc.

Description of random sequences in strongly-correlated systems with the help of β - distribution has been considered. This new method was applied to analysis of CCD-matrix noises recorded at different temperatures. Every noise sequence was "read" in terms of fitting parameters of the β - distribution. Relative fitting error does not exceed the value of 2.2% with the value of Pearson correlation coefficient close to 1. The fitting parameters are rather stable to a difference in treatment procedures. In first treatment method the procedure was applied to the mean values of the noise sequence, while in the second - to each separate sampling with subsequent averaging in the end. For the first method the relative error is located in the vicinity of 1%, while for the second approach this value is about 2.2%. This simple comparison confirms that the self-averaging phenomenon occurs as a result of repetition of the same measurement. With the help of the ECs method we recognized a hypothesis for temperature behavior of the mean values that were calculated for each sampling. This hypothesis represents itself in a linear combination of two exponential functions. One can judge about the temperature stability of the CCD device analyzing the fitting parameters with respect to the temperature. The method has potential application in device calibration or in determination its readiness to a normal work.

Laser optical response of NiO nanostructered films doped with oxidized silver nanoparticles in spectral range of 633-700 nm under the action of carbon monoxide has been revealed. Increased sensitivity of laser induced optical response to carbon monoxide has been demonstrated by micro and nanostructured NiO films modified with silver oxidized nanoparticles. Absorption and diffuse reflection spectra data of composites were used to determine compounds of the composite (Ag₂O, NiO, Ag). The sensitivity of the gas action and its dependence on the film microstructure are shown and discussed.

All-adaptive imaging of phase objects in focusing of spatially phase-modulated laser beams in an extended weakly absorbing liquid or a gas medium is realized. The required level of the system operation corresponds to the initial stage of thermal self-action of the illuminating laser beam. Imaging occurring in an extended weakly absorbing medium in a definite power range is a new effect in propagation of spatially phase-modulated laser beams. Imaging of objects in such schemes takes place in focusing of a spatially phase-modulated beam of an appropriate power directly on a real weakly absorbing atmosphere or an aqueous medium. Due to adaptivity of this nonlinear process in contrast to linear systems, imaging occurs under the conditions of heat flows, which leads to wandering of the laser beam waist as a whole in the Fourier plane.

Generators with inductive energy storage (GIES) are developed for laser application. Discharge and laser parameters in high-pressure gas mixtures are studied. It was shown that the IES generator produces high-voltage pre-pulse and sharp increase of discharge current which allows to form long-lived stable discharge in different gas mixtures. Improve of both pulse duration and output energy was achieved for XeCl-, XeF- and KrF excimer lasers. Maximal at that date radiation power, output energy and laser pulse duration of N₂ laser were obtained. Efficient operation on CO₂ molecules with high peak power was demonstrated. Ultimate efficiency of HF(DF) non-chain lasers was achieved.

An overview is given about experiments with a new method for Q-switching lasers at a constant pulse repetition frequency. It uses inside the laser resonator a Single Crystal Photo-Elastic Modulator (SCPEM). This consists of one piezo-electric crystal electrically excited on a mechanical resonance frequency. In resonance mechanical stresses are induced that lead via the photo-elastic effect to a strongly modulated birefringence. Polarized light going through such an oscillating crystal will experience a significant modulation of its polarization and of transmission through a polarizer. Suitable materials should not be optically active, as it is for example the case for SiO₂, and should allow the excitation of a longitudinal oscillation with an electric field perpendicular to the travelling direction of the light. Crystals of the group 3m, like LiTaO₃ and LiNbO₃, proved to be ideally suited for SCPEMS for the NIR- and VIS-region. For the infrared GaAs can be used. We demonstrated SCPEM-Q-switching for a Nd:YAG-fiber, a Nd:YVO4-slab- and a Nd:YAG-rod-laser with typical pulse repetition rates of 100-200kHz, pulse enhancement factors of ~100 and pulse durations ~1/100 of the period time. Typically the average power during pulsed operation is nearly the same as the cw-power, when the modulator is switched off. The most stable results were achieved up to now with the Nd:YVO4-slab-laser at 10W average power, 1.1 kW peak power, 127 kHz pulse repetition rate, and 70ns pulse durations.

Results are presented of a comparative numerical study of continuous-wave chemical DF laser with ramp and equivalent slot nozzle arrays. A special code is developed and is used to calculate the spacial distribution of chemical species accounting for the stimulated emission in the Fabry-Perot resonator. Influence of the design principles of these nozzles on lasing performance is investigated under different flow conditions in the active medium.

The parameters of a periodic-pulse planar CO₂-laser pumped by microwave (MW) discharge at a frequency of 2.45 GHz have been studied experimentally. The laser comes in two versions with longitudinal discharge- gap lengths of 250 (version A) and 470 (version B) mm. An average output power of 60 W could be achieved at a wavelength of 10.6 μm. The peak output power in the periodic-pulse mode of operation is about 1300 W. The shape and energy of the laser pulse have been investigated as a function of nput power, working mixture composition, pressure, repetition frequency and duration of microwave pumping pulses.

Compact slab repetitively-pulsed RF discharge overtone CO laser is developed. Results of parametric study of the laser with cryogenically cooled electrode system operating in sealed-off mode are reported. The average output power of the laser was up to 0.5 W with maximal efficiency of ~1.5 %. More than ~80 ro-vibrational overtone CO laser lines (summarizing two spectral ranges 2.5-3.1 μm and 3.1-4.2 μm corresponding to two sets of laser resonator mirrors used in the experiments) were observed. Start-up experiments on development the laser head of new design with enlarged active medium length (40 cm) were carried out. Preliminarily the output power of the overtone CO laser with the new laser head reached 0.75 W at the efficiency up to 1 %.

Experimental and modeling results on CO laser frequency conversion are presented. A Q-switched multiline CO laser with pulse repetition rate 20-150 Hz of sub-microsecond pulses and electron beam sustained discharge frequency-tunable mode-locked CO laser were used in the experiments on second harmonic generation (SHG) in high-quality ZnGeP₂ and GaSe crystals. Internal SHG efficiency exceeded 12.4 % in 12 mm ZnGeP₂ crystal. The SHG in 4 mm GaSe crystal was observed with internal efficiency of 0.3%. A possibility of difference frequency generation of fundamental and firstovertone CO laser lines to cover spectral range of ~4.0-5.0 μm is discussed. It is estimated that the difference frequency generation of neighboring lines of both fundamental and first-overtone bands allows one to obtain oscillation in THz spectral range within ~200-3000 μm.

The technology for manufacturing active elements for high-power (more than 1 kW) Yb³⁺:YAG disk lasers has been developed. A series of disk active elements with a thickness of 200...400 μm, a diameter of 8...15 mm, and a Yb³⁺concentration of 8...15 at. % has been created. A model of a CW disk laser with an output power of 45 W, an optical efficiency more than 45%, and a pump power density more than 2.5 kW/cm² has been made.

Nonuniform temperature distribution inside the nonlinear-optical crystal heated by the high-power laser radition is characterised by the equivalent crystal temperature, which is directly determined from the measured frequency of the crystal piezoelectric resonance.

A model of nonlinear-optical crystal heating is proposed that enables one to determine temperature distribution inside the sample under action of laser radiation from the measurements of internal crystal temperature. Absorption and heat transfer coefficient at crystal-air boundary are also determined. Crystal temperature is measured by analyzing changes of piezoelectric resonance frequencies of the sample.

Germany's leading role in laser technology is not least a consequence of successful national precompetitive joint development projects between industry and science: Funding of laser technology in Germany is strongly performed by the German Federal Ministry of Education and Research (BMBF) and has already been started in the second half of the eighties of last century. Since then several programs matched to the actual technological status and the future requirements of the market have been run: whilst activities have been focused on gas lasers in the beginning, today - in the actual research funding program "optical technologies" - semiconductor lasers and diode pumped lasers are in the center of interest. More than ever before relevance of the development to applications must be integrated into the projects. Consequently, in most projects lasers source development and application of novel brilliant laser sources are combined. This has been successfully performed in the BRIOLAS (Brilliant Diode Lasers) initiative, which has been launched in 2004 and will come to an end in 2010. Based on the knowledge and experience gained in the 13 projects of the BRIOLAS initiative, two new initiatives have been launched in 2008, namely INLAS (Integrated Optical Components for High Power Laser Beam Sources) and MABRILAS (Material Processing with Brilliant Laser Beam Sources).

Automotive components are for the most part cylindrical and thus the weld seams are of radial shape. Radial weld seams are usually produced by starting at a point on the component's surface rotating the component resulting in an overlap zone at the start/end of the weld. In this research, it is shown that the component's distortion strongly depends on the overlap of weld start and end. A correlation between overlap zone and distortion is verified by an experimental study. In order to reduce distortion generated by the overlap zone a special optics is used which allows shaping the laser beam into a ring shape which is then focused on the cylindrical surface and produces a radial ring weld seam simultaneously by one laser pulse. In doing this, the overlap zone is eliminated and distortion can be reduced. Radial weld seams are applied on precision samples and distortion is measured after welding. The distortion of the precision samples is measured by a tactile measuring method and a comparison of the results of welding with the ring optics to reference welds is done.

Ti-alloys used in prosthetic applications are mostly alloys initially developed for aeronautical applications, so their behavior was not optimized for medical use. A need remains to design new alloys for biomedical applications, where requirements such as biocompatibility, in-body durability, specific manufacturing ability, and cost effectiveness are considered. Materials for this application must present excellent biocompatibility, ductility, toughness and wear and corrosion resistance, a large laser processing window and low sensitivity to changes in the processing parameters. Laser deposition has been investigated in order to access its applicability to laser based manufactured implants. In this study, variable powder feed rate laser cladding has been used as a method for the combinatorial investigation of new alloy systems that offers a unique possibility for the rapid and exhaustive preparation of a whole range of alloys with compositions variable along a single clad track. This method was used as to produce composition gradient Ti-Mo alloys. Mo has been used since it is among the few elements biocompatible, non-toxic β-Ti phase stabilizers. Alloy tracks with compositions in the range 0-19 wt.%Mo were produced and characterized in detail as a function of composition using microscale testing procedures for screening of compositions with promising properties. Microstructural analysis showed that alloys with Mo content above 8% are fully formed of β phase grains. However, these β grains present a cellular substructure that is associated to a Ti and Mo segregation pattern that occurs during solidification. Ultramicroindentation tests carried out to evaluate the alloys' hardness and Young's modulus showed that Ti-13%Mo alloys presented the lowest hardness and Young's modulus (70 GPa) closer to that of bone than common Ti alloys, thus showing great potential for implant applications.

The paper reports about the results of researches of nanopowder production with a help powerful repetitively pulsed CO₂ laser "LAERT" which generated radiation with pulse energy of ≈1 J, peak power of ≈8 kW and mean power of 500 W. Laser radiation affected and evaporated the target. The target material vapor condensed into nanoparticles as a result of intermixing vapor with a flow of cold gas. In basic the air of atmospheric pressure was used as the carrier gas. However in some experiments were used He and Ar and the gas pressure also was changed. In our experiments we produced nanopowders of such materials as: YSZ, YSZ:Al₂O₃, Al₂O₃, CeO₂:Gd₂O₃, 0.5%Nd:Y₂O₃, 1%Nd:YAG, Fe₃O₄and carbon with a middle size 10÷30 nm. Received nanopowders were also weakly agglomerated. We carried out 3D numerical modeling of thermo-hydrodynamic processes occurred during the laser evaporation of a target. Results of calculations have cleared up many details of target evaporation. In particular, influence of liquid melt movement on stoichiometry of evaporation of a target from oxide mixes is found out. Results of calculations are in a good agreement with experimental data.

Direct laser sintering of a mixture of two metal powders with significantly different melting points is investigated by numerical simulation. The model is based on self-consistent non-linear continuity equations for volume fractions of components and on energy transfer equations for the powder mixture. It includes the movement of the solid particles due to shrinkage because of the density change of the powder mixture and the liquid flow driven by the capillary and gravity forces. The liquid flow is determined by Darcy's law. The effect of surface settlement of the powder is obtained. The width increasing rate of the melting zone depend both on the parameters of the laser radiation (on the power of the beam) and on the physical parameters of the particle's material, and it increases with the increasing of the penetrability or the increasing of the phase-transition heat. The increasing of the laser power under other factors being equal results in the acceleration of the melting front propagation.

In our previous work we found experimentally the scaling laws for the oxygen-assisted laser cutting of low-carbon steel of 5 - 25 mm. No dross and minimal roughness of the cut surface were chosen as criteria of quality. Formulas were obtained to determine the optimum values of the laser power and cutting speed for the given sheet thickness. In the present paper, the energy balance of the oxygen-assisted laser cutting is studied experimentally at these optimum parameters. The absorbed laser energy and heat conduction losses and cut width were measured experimentally, and then the energy of exothermic reaction of oxidation was found from the balance equation. To define the integral coefficient of absorption, the laser power was measured on the cutting channel exit during the cutting. The heat conduction losses were measured by the calorimetric method. It has been established that the absorbed laser energy, oxidation energy, thermal losses and melting enthalpy related to a sheet thickness unit, do not depend on the sheet thickness at the cutting with the minimal roughness. The results enable to determine the fraction of the oxidized iron in the melt and thermal efficiency at the cutting with the minimal roughness. The share of the oxidation reaction energy is 50 - 60% in the total contributed energy.

Numerical comparisons of some models for estimating the power losses due to heat conduction in process of gas-assisted laser cutting are presented in this paper. In spite of differences between these models their results match fairly well.

High energy ion generation (energy in order of 10 Gev) have been estimated by interaction of picosecond laser pulses with an intensity of 6x10¹⁴ W/cm² with metallic target in vacuum and gas atmosphere. In this paper we shall discuss the production of very high magnetic fields by flux compression in laser-induced plasmas and show experimental results on particle acceleration due to an explosively collapsed magnetic fields. Different nuclear track detectors have been used for heavy charged particle identification: synthetic mica, plastic nuclear detector CR-39, and glasses. Magnetic fields generated in laser-induced plasmas of order 30 -130 MGauss have been estimated by means of Faraday rotation and interferometric diagnostics with high temporal and spatial resolution.

Strong effect of steel hardness on the parameters of laser-induced plasma (e.g., temperature) and on the calibration curves for manganese and chromium in steels has been demonstrated. The presence of the inverse correlation between the steel hardness and the excitation temperature determined by Mn I lines was explained by the confinement of laser plasma with the crater walls. A new calibration strategy based on the summation of intensities for several lines of the analyte allowed one to reduce the effect of matrix, caused by mechanical properties, on the determination of chromium and manganese in steels. The advantages of this strategy are discussed in the article in comparison with the wellestablished approaches, such as an internal standard and single analytical line.

The interaction of ultra-high intensity laser pulses with solid targets is studied theoretically and with Particle- In-Cell (PIC) simulations. The regime of Radiation Pressure Acceleration of ultrathin foil targets is investigated within an improved "Light Sail" or "accelerating mirror" model. The latter provides simple and useful scalings for the characteristics of accelerated ions. The underlying dynamics, unfolded by PIC simulations, is however more complex than the simple model may suggest. An important issue is the heating of electrons that, even if strongly reduced by the use of circulary polarized (CP) pulses, may lead to a significant broadening of the ion spectrum. Radiation Reaction (RR) effects in the ultra-relativistic regime of extreme intensities are included in the PIC simulations via the Landau-Lifshitz formula. Apparently, for linearly polarized pulses RR slightly reduces the ion energy but also contributes to cooling the electrons, while RR effects are rather weak for CP pulses.

Quantum electrodynamics (QED) in strong laser fields is a vivid area of research, which will soon become systematically testable experimentally. We present analyses of three aspects of strong-field QED: First we show that the precise shape of ultra-intense few-cycle laser pulses is determinable via nonlinear Compton scattering and second that due to photon-photon interactions mediated by the quantum vacuum it is possible to set up a double slit experiment comprising only light. Finally we consider nonperturbative electron-positron pair creation.

Results of 2DMonte-Carlo simulations of development of QED cascades in intense uniformly rotating electric field are presented. We consider cascades produced by initially slow electrons. It is shown that under such conditions stable cascade development starts at field strength of the order of 1% of the QED critical field 5 × 10²⁹W/cm². The cascade yield is growing exponentially in time. Several characteristics of cascade, including average energy of particles and their mean free path times are computed. Our results are in good agreement with recent estimations [A. M. Fedotov et al., PRL 105, 080402 (2010)].

Electron-positron pair creation is among the QED-effects known to occur in a strong laser pulse interaction with a counter-propagating electron beam. In this regime multiple pairs may be generated from a single beam electron, some of the newborn particles being capable of further pair production. Radiation back-reaction prevents avalanche development and limits pair creation. The system of integro-differential kinetic equations for electrons, positrons and γ-photons is solved numerically.

Comparative analysis of optimal scheme of non-collinear optical chirped-pulse parametric amplification of fewcycle femtosecond pulses from Ti:Sa laser in LBO and DKDP crystals pumped by picosecond pulses up to petawatt level is presented. A flexible code, based on the extended model of parametric amplification, which takes into account the large set of effects such as saturation, phase self-modulation, influence of beam divergence, thermal effects, and amplification of spontaneous emission was realized. A way of creating nearly 1 PW system based on LBO crystals with transform-limited pulse duration about 9 fs has been demonstrated. Comparison between DKDP and LBO crystal showed that the latter is much better for OPCPA petawatt system design than DKDP.