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Herein, on the basis of expressions for the refractive indices of isonormal waves, the possibility of performing collinear phase matching for optical parametric generation in arbitrary directions of a biaxial KTA crystal under pumping by radiation of a YAG:Nd laser is analyzed. The tuning curves that determine the tuning range of the signal and idler for type-I and II-type phase-matching and arbitrary angles θ and φ in cases where the tuning is carried out along the angle θ at a fixed angle φ and vice versa are calculated. The effective nonlinear coefficient is determined. It is shown that their maximum value is achieved аt a polar angle θ = 90° and type-II phase-matching. For the case of generation of eye-safe radiation the spectral and angular phase matching widths were estimated, as well as gain widths of KTA-OPO under monochromatic pumping.

In this paper, we present the results of the study of the statistics of pulse energy fluctuations in a Raman laser under optical pump by the multimode nanosecond pulses. A system of coupled differential equations for slowly varying envelopes of the pump field and first three Stokes lines was integrated numerically with taking into account spatial inhomogeneity of the pump beam, spontaneous noise, and optical feedback. Data of the numerical simulation revealed a sharp increase in the fluctuation amplitude in the nonlinear regime of Raman frequency conversion when the optical length of the Raman cavity was matched with the cavity length of the multimode pump laser. At a mean 1st Stokes conversion efficiency of 3.5–3.8 %, the calculations showed an increase in the coefficient of variation (CV) of a random value from 9 % to 118 %. In the linear regime of Raman frequency conversion, when the conversion efficiency was 0.2–0.03 %, a further increase in the CV value up to 270–500 % was predicted. It is also numerically shown that the fluctuation statistics under the conditions of the cavity length matching is essentially non-Gaussian and described by the L-type probability density distributions (PDDs) with long tails and maxima located near zero. The numerical data were quantitatively confirmed by an experiment for a Raman laser on a barium nitrate crystal operated near the Raman threshold, when the 1st Stokes conversion efficiency did not exceed 0.3 %. A Raman cavity was formed by two flat mirrors providing a double-pass pump configuration. The Raman laser was excited by the linearly polarized frequency-doubled radiation of a Q-switched Nd:YAG laser generating multimode pulses with a duration of 7–8 ns. A Raman laser operating regime characterized by the hyperexponential PDDs with CVs reaching 480 %, which is 2–2.5 times higher than those observed earlier for the single-pass conditions of stimulated Raman scattering, was realized.

Using pulses of multifrequency stimulated Raman scattering (SRS) in calcite, nonlinear photoluminescence in a stilbene molecular crystal is excited. When multifrequency SRS is excited by the radiation of a Nd3+ : YAG laser with a wavelength of 1064 nm, eleven anti-Stokes components are observed in the visible spectrum with an average frequency shift of 1086 cm−1 between them. Using the second harmonic of the Nd 3+ : YAG laser radiation allowed three anti-Stokes and four Stokes components to be recorded. The large spectral range of the frequency comb facilitated effective reduction in the duration and increase in the intensity of the radiation pulse of multifrequency SRS.

Stimulated Raman scattering (SRS) of picosecond laser radiation at 532 and 355 nm in microcrystalline powders of potassium, sodium, and strontium nitrates has been studied. One anti-Stokes and three Stokes components were generated in all samples when pumping at 532 nm. For the first time to our knowledge, random Raman lasing in the used nitrates has been obtained upon their excitation at 355 nm. In this case, the multifrequency Stokes SRS is also observed in all nitrates. We have analyzed all possible loss channels when ultraviolet radiation is used for excitation of SRS. In general, picosecond random SRS generation has been obtained at 19 spectral lines in the spectral range of 360–630 nm. In all cases, the SRS process is due to the internal symmetric mode of the (NO3)− ion with the frequency shifts of 1050 cm−1 (KNO3), 1069 cm−1 (NaNO3), and 1057 cm−1 (Sr(NO3)2).

Nonlinear refraction in a number of crystals (KGW, KGW:Eu3+, Ba(NO3)2, BaWO4, PbMoO4, and CdWO4) that are promising for excitation of multifrequency stimulated Raman scattering is investigated by a single-beam Z-scan method. Picosecond laser pulses with a wavelength of 1064 nm generated by a YAG:Nd3+ laser were used for excitation of nonlinear optical processes. The values of n2 are compared depending on the type of the crystal, optical-axis orientation, and impurity concentration.

The Raman spectra of different specimens of protium and deuterium water have been compared. The spectra have been recorded using a fiber-optic technique and a compact BWS465-785H spectrometer. The spectra of spontaneous Raman scattering have been excited using a cw laser with a wavelength of 785 nm. Significant differences in the low-frequency Raman spectra from different specimens of water have been observed, which were explained by the presence of structural changes and impurities in analyzed specimens. Stimulated Raman spectra in protium and deuterium water have been measured upon excitation by picosecond laser pulses at a wavelength of 532 nm. The presence of low-frequency satellites in the spectrum of stimulated Raman scattering, indicating the structuring of water due to the formation of clusters consisting of a few molecules, has been revealed.

The spectra of multifrequency parametric stimulated Raman scattering in a barium nitrate single crystal is investigated. When this single crystal is excited by ultrashort (80 ps) YAG : Nd3+ laser pulses with a wavelength of 1064 nm, a frequency comb of eight anti-Stokes components is observed in the visible spectral range. The Raman satellites are due to the totally symmetric vibrational modes of barium nitrate single crystal. The frequencies of the corresponding Raman Stokes components in the IR range (from 1193 to 9662 nm) are calculated. The results of the study open the way to form an array of laser frequencies from the IR to green spectral range with a period of 1047 cm–1.

Stimulated Raman scattering in water and liquid nitrogen is studied near the liquid-air interface at picosecond (15 and 57 ps) laser excitation. For the first time, it is shown that Raman threshold on the interface is crucially reduced (up to 30-fold due to the effect of new liquid Raman laser discovered by us) in comparison with the bulk liquid, and the new spectral component at the interface of water-air near 3000 cm−1 is appeared as a parametric ring around the known axial beam component at 3400 cm−1.

The 1st Stokes pulse energy fluctuations of a solid-state Raman laser was found to describe by essentially non-Gaussian statistics if the length of its cavity is matched with that of a nanosecond multimode pump laser. The observed statistical data are discussed within the framework of developed numerical model.

In this work we report the spectroscopic properties of Tm3+:NaBi(MoO4)2 crystals with the dopant concentrations of 0.7 at.% and 3 at.%. The energy levels of the Tm3+ in the NaBi(MoO4)2 host were determined from polarized optical absorption and photoluminescence spectra measured at 77.4 K. Radiative properties of the crystals were calculated in context of Judd-Ofelt theory. Raman spectra of the crystal were studied. The concentration dependences of emission decay times of 3H4 and 3F4 levels were analyzed. The potential of the crystal for building tunable and ultrafast pulse lasers is shown on the base of cross sections and gain coefficient in the range of 1.9 μm.

This is a comparative study of eye-safe extracavity KGd(WO4)2 (KGW) Raman lasers that convert multimode emission from pulsed Nd:KGW lasers operating on the 4F3/2 → 4I11/2 and 4F3/2 → 4I13/2 transitions into the third Stokes component at λ = 1500 nm and the first Stokes component at λ = 1507 or 1538 nm. For equal sizes of the Raman and laser sections of a Raman laser emitting the third Stokes component, the pulse energy is higher (~14.2 mJ) and the divergence of the Stokes beam is lower (~9.4 mrad) for a lower energy of the Nd:KGW laser (~6.7 J). For pump pulse energies of 29–34 mJ, all the Raman lasers have essentially the same optical lasing efficiency of up to 36%. In terms of the electrical energy delivered to the flashlamp, however, the overall efficiency of the Raman laser for the third Stokes component is a factor of ~1.7 higher. The duration of the Raman pulses is comparable to that of the pump pulses and is ~20 ns for the first Stokes components. The pulse in the third Stokes component is shorter by a factor of 2.5–3. Given the different pump levels and the differences in the thermallyinduced optical distortions of the Nd:KGW laser components, the energy density distribution for beams of the first Stokes components is elliptical, while that of the third Stokes components is almost circular. The possibility of simultaneous lasing at wavelengths of 1507 and 1538 nm with parallel and mutually orthogonal polarizations of the Stokes waves is demonstrated.

A system of equations is constructed for the power of the Stokes components generated individually or simultaneously by a steady-state Raman laser. Examples of lasing in one, two, or three components are used to show that these equations can be used in a simple way to optimize the operation of this type of laser system.

The shape of the multimode Stokes pulse generated by an eye-safe KGd(WO4)2:Nd laser with self-frequency Raman conversion and active Q-switching was shown to depend on the inhomogeneity of the active-medium pump. The laser generated a short and undistorted Stokes pulse of length ~2.5 ns that increased with increasing laser cavity length for a moderately inhomogeneous pump characterized by a higher population inversion in the center of the active element. The energy of the Stokes pulse (~11.5 mJ) varied little as the output-mirror reflectivity varied in the range 5–45%. The Raman pulse became distorted if the inhomogeneity of the pump was increased considerably. The degree of pump inhomogeneity was negligible with fundamental TEM00 mode selection. The laser generated subnanosecond Stokes pulses with peak power in the MW range.

A passive way of eliminating optical feedback between a pump laser and an extracavity two-pass pumped Raman laser in a compact arrangement was demonstrated. Feedback was suppressed by arranging the circuit elements in a configuration where the pump-laser 100% mirror and the Raman-laser output mirror formed an unstable cavity characterized by a substantially higher threshold for generating the fundamental radiation as compared with the stable pump-laser cavity. The method was demonstrated using an eye-safe KGd(WO4)2 Raman laser pumped by a pulsed KGd(WO4)2:Nd laser with the working transition $$ {}^{{}^4}F_{3/2}\to {}^4I_{13/2} $$ as an example. The Raman laser emitted pulses of energy ~11.5 mJ at an electrical pump energy of ~10 J, corresponding to a conversion efficiency of ~31%. The Stokes pulse width (~17 ns) was comparable to the pump pulse width (~20 ns) owing to the extracavity location of the Raman laser.

We report on highly-efficient room-temperature lasing in 5at.%Tm:KLu(WO4)2 mini slabs with Nm and AT orientations side-pumped by a 50W diode bars. CW maximum output power of 16.7 W at 1910 nm has been demonstrated with optical and slope efficiencies being of 35% and 45%, respectively.We report on highly-efficient room-temperature lasing in 5at.%Tm:KLu(WO4)2 mini slabs with Nm and AT orientations side-pumped by a 50W diode bars. CW maximum output power of 16.7 W at 1910 nm has been demonstrated with optical and slope efficiencies being of 35% and 45%, respectively.

For the first time, using sturgeon sperm as a model system, sensitive to optical radiation, the comparative studies of biological effect of continuous wave, quasi-continuous wave, nano- and picosecond laser radiation under conditions with equal average irradiance (3 mW/cm2) and wavelength (532 nm) have been carried out. Analyzing the parameters of spermatozoa motion it has been shown that, depending on the energy dose and mode of laser operation, the radiation may have both stimulatory and inhibitory effect on the velocity of motion and spermatozoa motility duration as well as on sustaining of functional characteristics of cold-stored sperm. The possibility of increasing the fertilization rate due to use of the sperm preliminary treated with laser radiation is demonstrated. For the first time, the possibility of enhancement of biological effect going from continuous wave to quasi-continuous wave laser radiation at equal irradiance and wavelength has experimentally been proven. It is shown that the difference in biological effect of continuous wave, quasi-continuous wave, nano- and picosecond laser radiation is due to amplitude (peak) values of intensity. Using fluorescence analysis and luminol-dependent chemiluminescence assay, evidence for the participation of endogenous flavins and metal-free porphyrins in sensitized ROS formation (singlet oxygen, hydrogen peroxide, and hydroxyl radicals) in sturgeon sperm was obtained. Mechanisms of photochemical and photothermal reactions explaining the difference in efficacy of action of laser radiation in above modes are discussed.

Ca9Nd(VO4)7 single crystal was grown by the Czochralski method in inert atmosphere. The crystal structure and chemical composition were studied. Polarized absorption and luminescence spectra were investigated in details. It was found that the Ca9Nd(VO4)7 crystals belongs to self-activated laser materials with a weak concentration quenching of luminescence. Judd-Ofelt analysis was performed. The emission cross-sections spectra for 4F3/2 → 4I9/2, 4I11/2, 4I13/2 transitions were determined. For the first time Raman spectra of the Ca9Nd(VO4)7 single crystal were recorded and interpreted.

Unpolarized spontaneous Raman spectra of crystalline double calcium orthovanadates Ca10M(VO4)7 (M = Li, K, Na) in the range 150–1600 cm–1 were measured. Two vibrational bands with full-width at half-maximum (FWHM) of 37–50 cm–1 were found in the regions 150–500 and 700–1000 cm–1. The band shapes were approximated well by deconvolution into Voigt profiles. The band at 700–1000 cm–1 was stronger and deconvoluted into eight Voigt profiles. The frequencies of two strong lines were ~848 and ~862 cm–1 for Ca10Li(VO4)7; ~850 and ~866 cm–1 for Ca10Na(VO4)7; and ~844 and ~866 cm–1 for Ca10K(VO4)7. The Lorentzian width parameters of these lines in the Voigt profiles were ~5 times greater than those of the Gaussian width parameters. The FWHM of the Voigt profiles were ~18–42 cm–1. The two strongest lines had widths of 21–25 cm–1. The vibrational band at 300–500 cm–1 was ~5–6 times weaker than that at 700–1000 cm–1 and was deconvoluted into four lines with widths of 25–40 cm–1. The large FWHM of the Raman lines indicated that the crystal structures were disordered. These crystals could be of interest for Raman conversion of pico- and femtosecond laser pulses because of the intense vibrations with large FWHM in the Raman spectra.

We report on growth and detailed spectroscopic study of Eu3+-doped tetragonal sodium gadolinium double tungstate, Eu:NaGd(WO4)2, a new promising crystal for deep-red lasers. Large-volume crystal doped with 4.9 at.% Eu is grown by Czochralski method along the [001] crystallographic direction. Absorption of Eu3+ ions is studied at room temperature (RT) and at 6 K. For the absorption band related to the 7F1 → 5D1 transition suitable for pumping of Eu:NaGd(WO4)2, the maximum cross-section is σabs = 1.2 × 10−21 cm2 at 535.5 nm with the full width at half maximum (FWHM) of 3.1 nm (at RT, for E || a polarization). For the 5D0 → 7F4 transition, the maximum stimulated-emission cross-section is σSE = 1.6 × 10−21 cm2 at 698.3 nm (RT, E || c polarization). Lifetime of the 5D0 state is 490 ± 10 μs (at RT). Under UV excitation, Eu:NaGd(WO4)2 provides intense red emission with CIE coordinates (x = 0.671, y = 0.329).

Transverse mode locking of the Stokes component generated in the mode of stimulated Raman scattering self-conversion by a pulsed diode end-pumped Nd:YVO4/Cr:YAG laser is implemented for the first time under conditions of frequency degeneracy of cavity modes.

We report on highly-efficient room-temperature lasing in 5at.%Tm:KLu(WO 4 ) 2 mini-slabs side-pumped by a 50W diode bar. CW output power of 16.7 W at 1910 nm has been demonstrated with optical and slope efficiencies being of 35 and 45%, respectively.

Up to 15 mW of continuous wave deep red laser output at 702 nm are demonstrated using an Eu-(7.6 at.%):LiYF 4 crystal under pumping with a frequency doubled Ti:sapphire laser at 393.5 nm.

We report on a comprehensive spectroscopic study of monoclinic Eu:KLu(WO4)2 crystal concerning its potential applications in red lasers. Optical absorption and stimulated-emission cross-section spectra are determined for this crystal for the principal light polarizations, E || Np, Nm and Ng. The maximum σSE corresponding to the 5D0→7F4 transition is 1.78×10−20 cm2 at 703.5 nm (for E || Nm). Spectroscopic properties of Eu:KLu(WO4)2 are modeled within the conventional Judd–Ofelt theory, as well as its modification for systems with an anomalously strong configuration interaction (ASCI), yielding absorption oscillator strengths, luminescence branching ratios for 5DJ→7FJ' transitions and radiative lifetimes of the 5DJ states. Photoluminescent properties of Eu:KLu(WO4)2 are studied under UV/visible excitation. Polarized Raman spectra are measured for Eu:KLu(WO4)2.

Stokes generation has been considered under the Fourier-limited nanosecond pulse excitation to find Raman gain coefficients in potassium-gadolinium tungstate. Data of numerical simulation under spontaneous Stokes initiation, light diffraction, and optical feedback have been compared with experimental results to reveal coefficient values of 14 ± 3 and 11 ± 3 cm/GW for the p[mm]p and p[gg]p sample orientations, respectively, at 532 nm wavelength.

We establish the regularities of changes in the spectra of stimulated Raman scattering in light water (H2O) and heavy water (D2O) under changing laser excitation regimes. We find several satellites occurring in Stokes and anti-Stokes regions at high pumping intensities. We study the spectra of stimulated Raman scattering in H2O and D2O under excitation by the second optical harmonic (532 nm) of a YAG: Nd3+ laser generating ultrashort (60 ps) pulses with a recurrence frequency of 20 Hz and a peak power of 10-100 MW. We show that intense spectral bands determined by both intramolecular modes of light/heavy water and intermolecular modes - librations or translations of the molecular characteristic of ice - occur in stimulated Raman scattering spectra upon an increase in exciting radiation intensity. Our experiments demonstrate the prospects of using the phenomenon of stimulated Raman scattering for developing coherent waves corresponding to intramolecular and lattice modes of light and heavy water. The phenomenon can also be used for developing a deuterium plasma with high effective temperature in the region of laser radiation focusing in heavy water and low-temperature water in the boundary region.

High-power cw and quasi-cw lasing at the fundamental and second harmonic frequencies is obtained from Nd:KGd(WO 4 ) 2 lasers based on Np- and Ng-cut crystals pumped longitudinally by a diode laser at 879 nm. Because of different crystal lengths, the limiting pump power beyond which the crystals undergo thermomechanical damage is 26.8 W for the N p -cut and 17.3 W for the N g -cut. At these pump powers the cw outputs at λ = 1067.2 nm are 9.4 and 5.4 W, respectively, and the N g -cut crystal output is TEM 00 at the fundamental frequency. With quasicontinuous pumping at a 10% duty cycle the instantaneous laser power reaches ~11 W for both cuts with a periodic duration of 10–20 ms. The differential lasing efficiency relative to the absorbed pump power is 66.4% for cw lasing and 77.4% for quasi-cw operation. With intracavity frequency doubling using a KTP crystal, better results were obtained with the N g -cut crystal because of its simpler thermal lensing. The maximum second harmonic power was ~1.1 W for cw operation and ~2.6 W for quasi-cw operation with a diode laser power of 27.3 W.

We have investigated the self-Raman and intracavity Raman frequency conversion of the end-diode-pumped acoustooptic Q-switched Nd:YVO 4 laser radiation to eye-safe radiation. The 1st Stokes oscillation in YVO 4 (Nd:YVO 4 ), KGd(WO 4 ) 2 , PbWO 4 , and Ba(NO 3 ) 2 crystals excited by the laser radiation at a wavelength of 1342 nm permits obtaining oscillations at 1524, 1496 or 1527, 1527, and 1562 nm wavelengths, respectively. We have obtained pulsed lasing with a repetition rate of 2–20 kHz, an output energy of 37–95 µJ, and a duration of 6–8 ns. We propose a model of the actively Q-switched intracavity Raman laser taking into account the real switching off/on times of the actively Q-switch and the excited state absorption in the active medium. We used this model to simulate the dynamics of the self-Raman Nd:YVO 4 laser. The proposed model gives results that agree fairly well with the experimental data.

The characteristics of stimulated Raman scattering in benzene and carbon disulfide introduced in pores of globular photonic crystals—opal matrices formed from close-packed balls (globules) of amorphous quartz (silica)—have been experimentally studied. Stimulated Raman scattering spectra have been excited by giant pulses of the second optical harmonic (532 nm) of a YAG laser. The spectra have been recorded in the direction of mirror reflection from the (111) growth surface of a globular photonic crystal at various angles of incidence (10°–70°) of laser radiation. It has been shown that the threshold of stimulated Raman scattering decreases sharply (by more than an order of magnitude) at a certain angle of mirror reflection and additional Stokes and anti-Stokes Raman satellites appear in the spectrum. The observed sharp decrease in the threshold of stimulated Raman scattering has been explained by an increase in the spectral density of the electromagnetic field in the surface region of the photonic crystal because of the approach of the spectral position of the stopband of the photonic crystal to the exciting line (532 nm) under variation of the angle of incidence of pump radiation on the (111) surface.

Monoclinic 2 at% Eu-doped KY(WO4)2 is grown by top-seeded solution growth method. Polarization-resolved absorption and stimulated-emission cross-section spectra are determined for this crystal. Spectroscopic properties of Eu:KY(WO4)2 are modeled within conventional Judd–Ofelt theory, as well as theory of f–f transition intensities for systems with anomalously strong configuration interaction, yielding absorption oscillator strengths, luminescence branching ratios and radiative lifetime of 5D0 state. The impact of excited-state absorption from this state on possibility of laser operation is discussed. Photoluminescent properties of Eu:KY(WO4)2 are determined. This crystal provides intense red emission with CIE coordinates x=0.670, y=0.329.

Multiple Stokes and anti-Stokes satellites were observed in the spectra of stimulated parametric Raman scattering of light in liquids and crystals when excited by picosecond laser pulses of a YAG: Nd3+ solid-state laser with generation wavelengths of 1064 and 532 nm. The Stokes combination satellites of the infrared range were detected as a result of their conversion into the visible spectral region. The results obtained are of interest for the development of the theory of parametric processes of stimulated Raman scattering of light in crystals and liquids, which is also important for creating efficient laser sources from the ultraviolet to the far infrared.

Multi-frequency stimulated Raman scattering spectra were recorded with excitation of infrared (λ0=1064 nm) emission of picosecond solid state laser. The registration of spectra was with the fiber-optic technique by minispectrometer at wide frequency region.

We present the results of an experimental study of the spontaneous and stimulated Raman scattering (SRS) spectra and luminescence spectra of light and heavy waters. Also we investigate various samples of light water. We show the possibility of using spectral methods to detect impurities in water and determine the degree of its structuredness, which can serve as an additional criterion of the water quality. We find a fine structure in the SRS spectrum of heavy water in the low-frequency region.

A method for determining absorption cross sections of chromium ions in the ground and excited states in addition to their concentration in Cr4+:YAG crystalline absorbers was presented. The method was based on a study of the saturation of absorption, the measurement of the absorber transmittance as a function of laser-pulse energy, and the modeling of this function that gave the best fit of the experimental data. Absorption cross sections and concentrations of chromium ions were determined for seven absorber samples. The χ2-confidence intervals and correlation matrices for those parameters were calculated. The parameters of different samples were shown to vary over rather wide ranges. Hence, it was necessary to characterize beforehand a specific absorber sample in order to calculate correctly the parameters of lasers with Cr4+:YAG absorbers.

We have studied the lasing characteristics of a Raman laser based on an Nd:KGW crystal, converting multimode emission of a pulsed Nd:KGW laser with working transition 4F3/2–4I13/2 (1351 nm) to Stokes components with wavelengths in the 1700–1800 nm range. We show that when the pump polarization coincides with the N m axis of the optical indicatrix of KGW (E || N m ), the conversion efficiency for converting the pump radiation to the single second Stokes component with λ ~ 1786 nm reaches 17.5%, which results in an ~6.6 mJ Raman pulse. For E || N g , the conversion efficiency increases up to 22.5% and generation of an ~15 ns pulse occurs on four Stokes components with wavelengths 1704, 1744, 1770, and 1786 nm due to involvement of 86 cm–1, 767 cm–1, and 901 cm–1 vibrational modes in the stimulated Raman (SRS) process. We have determined the spectral distribution of the pulse energy. A total of 11 Stokes components are generated with participation of the indicated vibrational modes.

We study stimulated Raman scattering (SRS) in liquids (water and ethanol) embedded into photonic crystals (artificial opals) under excitation with 60 ps laser pulses at 532 nm. We observe a substantial decrease of the SRS threshold when the focused laser beam excites the crystals near their surface. The spatial distance between the beam center and the surface of the crystals is close to their nanoscale structure. The decrease in the SRS threshold is due to a substantial increase in the photonic-state density near the edges of the photonic crystal stop zones and the so-called Mie resonances in active media near the nanosized globules. This leads to a considerable increase in the local-electric-field intensity, causing the SRS threshold reduction. Such a method of reducing the SRS threshold opens up a way of creating new efficient laser sources based on photonic crystals and their use for different applications in nanotechnologies.

The $$\hbox {Ca}_{9}\hbox {RE}(\hbox {VO}_{4})_{7}$$ (RE $$=$$ La, Nd, Gd) and $$\hbox {Ca}_{10}\hbox {M}(\hbox {VO}_{4})_{7}$$ (M $$=$$ Li, Na, K) single crystals have been grown by the Czochralski method. The binary vanadates are isostructural to “whitlockite” mineral (rhombohedral symmetry, R3c space group). Their thermal conductivity has been investigated in the range 50 K–300 K parallel to the c axis. For $$\hbox {Ca}_{9}\hbox {Gd}(\hbox {VO}_{4})_{7}$$ crystals, the thermal conductivity has been investigated in the range 300 K–550 K also. Additionally, for the $$\hbox {Ca}_{10}\hbox {M}(\hbox {VO}_{4})_{7}$$ (M $$=$$ Li, Na, K) crystals the heat capacity has been studied in the temperature range 80 K–300 K. The character of the temperature dependence of thermal conductivity is close to that of glasses. The possible reasons of the observed features of the thermal conductivity have been analyzed. Raman spectra of $$\hbox {Ca}_{10}\hbox {M}(\hbox {VO}_{4})_{7}$$ (M $$=$$ Li, Na, K) crystals have been measured and discussed. The spectral lines were broad and similar to polycrystalline or amorphous solids. These crystals are expected to be suitable for application as efficient nonlinear optic and laser materials.

Experimental and numerical data on Stokes generation under the spectrally-limited nanosecond pulse excitation are collated to find the steady-state Raman gain coefficients. The approach is tested for barium nitrate. For potassium-gadolinium tungstate, the coefficients values of 14±3 and 11±3 cm/GW are determined in the p[mm]p and p[gg]p sample orientations, respectively, at 532 nm wavelength.

In eye-safe ring optical parametric oscillator (OPO) containing three KTiOPO 4 crystals the crystal placed first in the path of pump radiation is subjected to the strongest thermal distortion caused by idler absorption. For the 10-Hz 35-mJ OPO, thermally induced lenses generate an increase in the signal beam divergence by 10% and moderate decrease in the signal energy.

The processes of transient Raman generation and Raman amplification in KGd(WO4)2 (KGW) crystals pumped by laser pulses with the width of about 150 fs were studied experimentally. For excitation, Bessel beams were used. Gaussian beams of Stokes and laser radiation were used at amplification stage. Raman shifts of 768 or 901 cm-1 were obtained depending on orientation of KGW crystals. For optimal conditions the gain was more than 100. The conversion efficiency of amplifying (pump) radiation into amplified Stokes radiation reached 50 %.

Comparative studies on SRS conversion of 1 kHz ultrashort laser pulses (0.9–1.2 ps) at 401 and 802 nm in circulated and non-circulated compressed methane and hydrogen were carried out in SRS generation (SRSG) and stimulated Raman amplification (SRA) modes. It was shown that circulation of the gases weakened substantially the thermal lens, which facilitated reaching higher efficiencies of radiation frequency conversion and improved the quality of the obtained beams. This effect was especially pronounced in SRA mode in methane. In this case, the spectrum of the amplified beam practically coincided with that of the seed (beam to be amplified) and the quality of the first Stokes beam was close to the diffraction limit.

We demonstrate a passively Q-switched all-solid-state laser system with intracavity Raman frequency conversion to the eye-safe spectral region. Laser oscillation at the 1.064 μm wavelength with a pulse repetition rate of several kilohertz was provided by a Nd:YAG crystal and a Cr:YAG passive absorber. Third Stokes oscillations at the 1.599 and 1.494 μm wavelengths were obtained in Ba(NO 3 ) 2 and PbWO 4 crystals with output pulse energies of 5 μJ and 6 μJ, respectively. The results of the numerical simulation of the pulse dynamics are in good agreement with the experimental data.

A method of calculation of continuous wave generation visible output power of solid state Raman laser was developed. The expressions for the power of second harmonic generation of the Stokes field and sum frequency generation of the Stokes and fundamental field as functions of pump power and other parameters of the laser system were obtained and analyzed. Parameters relations at which output powers are maximal and the ones at which suppression of Stokes oscillation by sum frequency mixing process occurs were found.

Analytical equations for the power of second-harmonic stationary generation or sum frequency mixing in a Raman laser with an intracavity nonlinear medium are developed and analyzed as functions of pumping mode and other parameters of the laser system. Parameter relationships providing the maximum output power and conditions for suppression of both stimulated Raman scattering by sum frequency mixing and; consequently, of sum frequency mixing itself are found.

Single transdermal laser irradiation of the tail vein of males of white mongrel rats with an average mass of 350–400 g in three different regimes has been carried out. The irradiation doses were chosen to be intermediate between therapeutic and surgical ones, and the radiation wavelengths were 806 nm and 2 μm. The dynamics of the packed cell volume, deformability and cytometric indices of erythrocytes, and of the plasma and blood viscosity have been investigated. The rheological and cytometric changes in the blood caused by the irradiation stayed for several days. The observed rheologial changes are due to the removal of irradiation-damaged erythrocytes and the arrival in the blood channel of young and highly deformable red cells.

Experimental and theoretical studies of the coupled-cavity diode-pumped Nd:YAG/Cr:YAG microchip lasers with intracavity Raman conversion of laser pulses in a Ba(NO3)2 crystal into two Stokes pulses have been made. Two lasers with a different cavity length have been investigated. The minimal pulse durations at the 2nd Stokes wavelength were ≈100 ps in the short-cavity laser at pulse energy of 5 μJ, and the pulse repetition rate reached 20–24 kHz. The laser and Stokes pulse dynamics, as well as the spatial intensity distribution of the laser and the 1st Stokes beams at the output mirror have been recorded. A model describing such coupled-cavity microchip Raman lasers has been developed. The numerically simulated laser and Stokes pulse dynamics, and the calculated pulse energy, duration, and repetition rate are in good agreement with the experimental data.

Raman frequency conversion of high average power pulsed Nd:YAG laser radiation into the near IR spectral region in a barium nitrate Raman laser was studied with the emphasis on thermal effects inside the Raman-active medium. The probe-beam technique together with numerical reconstruction, done by integrating the transient heat conduction and paraxial wave equations, revealed dynamics of the induced distortions featuring high-order optical aberrations. By utilizing the Zernike expansion of the reconstructed phase profile and implementing a special focusing geometry of the pump beam, partial compensation of the distortions was realized in a stable configuration of the Raman cavity. Generation of the first-, second-, and third-order Stokes radiation with output power of 17, 9.5, and 5.5 W corresponding to a quantum conversion efficiency of 32, 21, and 13% is reported.

We used the single-beam Z-scan method, employing picosecond laser pulses with λ = 1064 nm, to measure the nonlinear refractive index and nonlinear absorption in vanadate crystals, which are promising for design of laser sources. We have established that there is practically no nonlinear absorption in these crystals in the near IR range and that doping them with neodymium ions leads to a significant reduction in the nonlinear refraction. This effect can be used to partially compensate for the negative impact of nonlinear refraction on the lasing characteristics of lasers.