We present different approaches to improve the beam quality of solid-state lasers. The original dual- or variable- configuration resonator was improved to emit completely polarized output. This was achieved by enforcing unidirectional operation due to the polarization dependence of the thermal lenses and of the gain in Nd:YVo₄ crystals. Single-frequency operation was obtained in a miniaturized version of this resonator based on a polarizing beam splitter made of Nd:YAG. Our transversally pumped high-power lasers feature output powers exceeding 600W. In order to compensate for the power dependent thermal lenses we investigate the use of self-adaptive compensating thermo- optical elements which generate thermally induced lenses with the opposite sign as the lense in the gain medium. Furthermore, to speed up the optimization processes we have derived a general analytical solution of the heat conduction equation for arbitrary heating distributions with cylindrical symmetry.

A high average power laser oscillator with a cavity completed by refractive index gratings that accompany population gratings induced in Nd:YAG laser crystals by generating beams themselves is investigated experimentally. The spatio-temporal self-adaptation of the cavity formed by nonlinear dynamic mirrors is studied. The possibility of compensating polarization distortions inside laser crystals is also investigated. The generation of beams with average power up to 250W, near-diffraction-limited divergence, and long coherence length is demonstrated.

The state and development prospects of diode-pumped solid- state Nd:YAG lasers are discussed using the devices developed by polyus RDI and Laser-compact company as examples. Low-power CW and Q-switched IR, green and blue lasers are successfully used for completing medical and industrial devices. The lasers operate in TEM00 mode with stability no worse than 2% per 8h of operation. Pulsed lasers providing a pulse energy of 50 mJ form the basis for a new generation of opto-electronic devices. The problem of stable operation of diode-pumped Nd:YAG laser within a wide operating temperature range is concidered.

An experimental studying of Nd:YAG rod side-pumping with quasi-cw-laser-diode bars as a function of the laser rod and the pumping sub-mount parameters was carried. We have found that the side-pump-of-rod geometry without coupler optics between the laser diodes and the laser rod provides sufficiently high slope and optical efficiencies of Nd:YAG laser. Utilizing the concentric pumping arrangement with eight laser diode bars maximum optical efficiencies of 50% and 45% in long pulse mode was obtained when 5mm and 4mm diameter Nd:YAG (1.2% at) rods respectively were used. In Q-switched operation Nd:YAG laser with this pumping scheme and 5mm diameter (1.2% at) rod had an output of 23 mJ in multimode 10 ns pulse when output coupler was of 60%.

Saturable absorber Q-switching of HO(superscript 3+:Y₃Al₅O₁₂ laser at 2.1 micrometers using PbSe-doped phosphate glass was demonstrated. Q-switched pulses of 22 mJ in energy and 85 ns in duration were obtained. Temperature dependence of luminescence spectra of phosphate glasses doped with PbSe Qds of different sizes was analyzed.

Efficient multi-wave generation in nanosecond regime SRS self-converter based on NaLa(MoO₄)₂:Nd³⁺ crystals by SRS-active mode (omega) equals 888 cm^-1 has been obtained. Also parameters of new miniature eye-safe SRS laser ((lambda) equals 1538nm) with self-conversion based on KGd(WO₄)₂:Nd³⁺ crystal is demonstrated. This laser has differential efficiency 0.3% by pump energy threshold about 1J.

Spatial-angular and spectral-energy characteristics of eye- safe lasing by SRS in barium nitrate, pumped by 1.32 micrometers Nd:YAG laser radiation in focused beams and resonator are studied. The pump-to-first-Stokes-component energy conversion factor 55% was obtained for lasing in resonator with single-mode pumping. With the multi-mode pumping essential gain in the lased radiation brightness compared with pump (beam clean-up) was received. It was shown that in the focused beams SRS take place in the wave-front replication mode. Thermal lens focal length in crystal was measured.

The theoretical and experimental study of eye-safe single- mode beam SRS amplification in the barium nitrate crystal at 1.32 micrometers Nd:YAG laser pump field with wide angular spectrum was performed. It was ascertained that most effective method for improving of Stokes beam divergence lies in inclining of the pump beam.

An investigation was made of several relationships governing excitation transfer in Cr-Yb-Er phosphate glasses. The activator concentrations were optimized. A family of the new erbium-doped laser glasses was developed.

The new laser crystals BeLaAl₁₁O₁₉ doped with Cr³⁺, Ti³⁺ and Nd³⁺ ions were grown by the Czochralski technique. The absorption and fluorescence spectra of impurity ions are reported and the temperature dependence of the fluorescence lifetime are described. The laser properties of these ions were investigated. The laser action has been achieved on ⁴F_3/2-⁴I_11/2 (1052 nm) transition of Nd³⁺ -ions under selective laser pumping. The physical properties of BeLaAl₁₁O₁₉ crystal were studied: the values of all independent component of elastic constant tensor were determined. On the base of a number of dynamic parameters of crystals, such as Young's modulus, the shear modulus, the volume elasticity modulus and Poisson's factor, Debye temperature and specific heat capacity were calculated. The investigation show that the BeLaAl₁₁O₁₉ is a promising host for a creature the new solid state laser media.

An influence of inter-ionic cross relaxation processes (up- conversion, self-quenching) on concentration and power dependence's of the inverse population of ⁴I_11/2 and ⁴I_13/2 laser levels in YLF:Er crystals under CW laser-diode pumping were studied both theoretically and experimentally. Computer simulations were carried out taking into account not only pair interaction but also the multi-ion interaction in the whole system. Optimal Er concentration for 3-micrometers CW lasing was estimated as 10- 15%.

We studied theoretically and experimentally the luminescence decay from excited erbium levels and laser action at 2.8 micrometers of lithium-yttrium double-fluoride LiYF₄:Er³⁺ (YLF:Er³⁺) crystals. Experimental studies of the luminescence decay curves were carried out using selective laser excitation at ⁴I_13/2 level by Q-switch pulsed Yb-Er glass laser ((lambda) _pumpequals1.53micrometers ). The spectroscopic model was developed to simulate the population kinetics of excited Er levels, emitting in VIS and IR spectral regions including the 3micrometers laser transition levels in YLF:Er³⁺ crystals. The rate equations for the six lowest energy levels of YLF:Er³⁺ were numerically solved for short pulse excitation. It is shown the theoretical and experimental results are in good agreement. Single mode CW laser action at 2.8-micrometers was demonstrated in YLF:Er₃₊ and Ba Y₂F₈:Er^3PLU crystals under LD pumping for the first time. Output power as high as 0.32 W and slope efficiencies about 20% were obtained with YLF:Er³⁺ (10%) laser rod in longitudinal pump scheme. No spike structure was observed in output beam. The dependence's of output power versus absorbed pump power were studied in laser rods with erbium concentrations10 at. % using LD pumping module (Model DL-5M) with fiber output.

Peak energy and intensity in absorption spectrum of (formula available in paper) (akermanite) were calculated by first-principles method, which we have developed. We investigated the dependence on size of cluster models with (formula available in paper) (without point charges added (formula available in paper) (with additional point charges), and (formula available in paper) models. All the models have low C_S symmetry at Cr^4- site. The best agreement with experimental spectrum was obtained in the larger (formula available in paper) model on the relative peak splittings which originate from the low symmetry, on the spectral anisotropy, and on the relative intensity. We conclude that the covalency between ligands and the outside cations have to be considered for the better description of spectrum in system with low symmetry.

We report on the results of lasing and spectroscopic investigations of the anomalously slow recoverable bleaching of Cr,Ca:YAG and Cr,Mg:YAG crystals. We propose two models for this effect: (i) Cr⁴⁺ reduction to Cr³⁺ due to oxygen valence band electron capture by Cr⁴⁺, and (ii) induced disorder in Cr⁴⁺ tetrahedral center due to effect of oxygen vacancies.

New saturable absorber Q-switch for 1.54 %mum Er: glass laser is present. The saturable absorber is transparent glass ceramic containing magnesium-aluminum spinel nanocrystallites doped with tetrahedrally coordinated Co²⁺ ions. Q-switched pulses of up to 5.5 mJ in energy and 80 ns in duration at 1.54 micrometers were achieved. Relaxation time of the ⁴A₂ to ⁴T₁(⁴F) transition bleaching was measured to be (450+/- 150)ns. Ground-state absorption cross-sections at 1.54 micrometers wavelength were estimated to be (3.2+/- 0.4)*10^-19 cm² and (5.0+/- 0.6)X10^-20 cm², respectively. Results of study absorption and luminescence spectra of different glass ceramics on the base of magnesium-aluminum, zinc-aluminum, lithium-aluminum spinel nanocrystallites doped with tetrahedrally coordinated Co²⁺ ions are also analyzed.

The theoretical calculation for nonlinear refractive index n₂ in Cr²⁺:ZnSe-active medium predicts the strong defocusing cascade second-order non-linearity within 2-3 micrometers spectral range. On the basis of this result the optimal cavity configuration for Kerr-lens mode locking is proposed that allows to achieve a sub-100 fs pulse duration. The numerical simulations testify about strong destabilizing processes in the laser resulting from a strong self-phase modulation. The stabilization of the ultra short pulse generation is possible due to spectral filtering that increases the pulse duration up to 300 fs.

We report on a complete technology ensuring fabrication of reliable electro-optical modulator employing Russian flux grown KTiOPO₄. The pilot units employing 2-crystals thermally compensated scheme, with aperture 4*4 mm², operate at 1.064 mkm both at AC and DC mode and exhibit at half-wave voltage about 1500V an extinction ratio up to 1:1000. No electro chromic damages were observed during multi hour testing.

Ion beam optical coatings based on titanium, tantalum and silicon oxides find wide application in visible and near IR lasers since they allow production of mirrors with a high coefficient of reflection as well as provide high laser damage thresholds. This paper reports on development of the coatings with low absorption and scattering and high coefficient of reflection (99.98%) at 632 nm for circular polarization and an angle of bean incidence of 45 degree(s) as well as on the protective antireflection coatings on BBO crystals and silicate glass at 1064 nm with high laser damage thresholds (15 . . .20 J/cm²). Absorption, scattering and loss in the mirrors as well as laser damage thresholds of the protective antireflection coatings have been measured.

High efficiency OPO has been designed for converting 1064 micrometers laser radiation into eye-safe region. Conversion efficiency 56.5% and threshold energy 2 mJ (0.06 J.sm²) have been achieved at repetition rate 12.5Hz. The divergence was less than 4 mrad up to 4 thresholds. With 180 mJ pump energy this converter can produce 70mJ output with efficiency 41% and low divergence at repetition rate 2.5Hz.

Theoretical and experimental studies the features of parametric generation light in LiNbO₃ with non-collinear phase matching from non-collinear angle i₂₃, i.e. angle between pump wave vector and resonant signal wave vector, are presented. It was shown that at the small angle i_{23<0,3 degrees} four nonlinear processes can simultaneously take place: these processes are non-collinear parametric conversion of the 1.0642 micrometers into the signal and an idler waves; second-harmonic generation of the signal; non- collinear difference-frequency mixing of the doubled signal and the idler; parametric conversion of the doubled signal into new pair: the signal and an idler waves. It is shown that the maximum efficiency of non-collinear OPO takes place for tangential phase-matching at (formula available in paper). Spectral broadening of the signal wave of LiNbO₃ non-collinear OPO was studied. Theoretically it is shown that the spectral bandwidth of the signal wave depends on the divergence of the signal wave.

In the present work the gain saturation effects in type-I BBO optical parametric amplifier (OPA) pumped by the 3rd harmonic of multi-mode Nd:YAG laser are investigated. The OPA gain was measured as a function of input idler energy at 1064 nm with a constant pump energy at 355 nm and a beam divergence 0,3 mrad. In the 9 mm BBO crystal at pump intensity approximately 68 MW.cm² and input idler intensity approximately 18 MW.cm² the efficiency of energy extraction in the saturated gain regime approximately 31% was obtained. The ways to increase the efficiency of energy extraction in the two-crystal OPA configuration are discussed.

Correlation between non-linear properties and optical quality of KTP crystals is investigated. Optical quality is investigated by the Schlieren method. The distribution of the mean-root-square refractive index gradient has been obtained along the radiation propagation direction. A comparison of optical quality of a crystal and the conversion efficiency is made. For the first time, the possibility of domain structure imaging in a crystal by using only an optical method is shown.

We derive the asymptotic behavior of the n^th order harmonic generation susceptibility using the Kubo response function formalism: it is characterized by a (omega) ^-2n-2 dependence and a coefficient proportional to the trace of the (n+1)^th derivative of the potential energy on the equilibrium density matrix. Using this result and the analytical properties of the susceptibility considered we derive new Kramers-Kroenig relations and sum rules. The general properties obtained show a strict correspondence with those already obtained with the classical anharmonic oscillator model.

Abnormal reflecting mirror (ARM) structures, consisting of a corrugated optical waveguide structure, can serve as a narrow band reflection filter in which strong field enhancement may occur by excitation of the guided mode. The latter is quite interest for SHG. We report experimental results of a first prototype, which exhibits CSHG in the ARM structure.

The problem of small particle size and material detection is important for industrial and environmental applications. Previous investigations have shown the possibility of using the laser breakdown method to achieve first goal; the sensitivity of this method is a thousand times higher than that of conventional methods. However, for small particle sizes, the damage threshold of the solid target in this case is very close to the breakdown point of pure air. After breakdown, there is a small volume of dense hot plasma that emits radiation. We analyzed this radiation especially at late stage using an analytical model and simulation code as well as by experiment, and found that the emission intensity varied depending on the laser type and plasma parameters including initial particle size.

The spectral characteristics and stability of a frequency of intermode beats of a femtosecond Ti:S laser are investigated. An active method is used to obtain high stability. The frequency stability of intermode beats not lower than 5.8.10^-14 rms in 100s is achieved. Possible applications of the setup, such as measurement of large frequency intervals in the optical range, creation of optical frequency synthesizers, etc. are proposed. The physical principles for the creation of an optical clock of a new type using highly stable femtosecond Ti:S laser are considered.

We describe our doubled YAG laser stabilized on the hyperfine structure of molecular iodine 127. We present the results in terms of stability and reproducibility and we will give a scheme of the scheduled absolute frequency measurement.

A Fabry-Perot-Michelson gravitational free mass interferometer is considered for a registration of the low frequency Earth gravity gradients. A variation of the Earth gravity force vector cause the corresponding misalignment of the interferometer mirrors thus providing information about the Earth gravity field. Gravitational interferometer with suspended mirrors provides a unique possibility to measure a relative angle variation between two plumb lines (gravity force vectors) separated by the large distance 3divided by4 km. So at very low frequencies the setup presents a long based angular gravity gradiometer for registering global geodynamics through the surface gravity gradient. A possibility of measuring the geophysical phenomena resulted in gravity field variations (core movements, Earth free oscillations, tidal harmonics, Earth rotation variations, etc.) Is discussed and technical requirements for the setup optical elements are formulated. Comparison with conventional geophysical devices is carried out. Estimates of the basic instrumental and seismic noises limiting sensitivity at low frequency (in the quasi-static regime) are discussed briefly. These estimates show that there is a hope for measurement of the gravitational angular perturbation of the mirrors at the level of 10^-12divided by10^-13 rad for the observation time about several hours. The possibility of arm signals reconstruction in the presence of recycling mirror is demonstrated. The auxiliary optical system for precise justification between up-down movements and tilts of the end spherical mirrors is considered. The requirements on the stability of laser system are discussed.

In this report, an interferometric method for measuring the parameters of the emitted light from a Step-Index Single- Mode optical fiber is introduced. A mirror oriented normal to the optical fiber axis is axially scanned in front of the fiber emitting face. The intensity of the resultant coupled back into the fiber interference is then detected. Interference fringes are used, as a tool, to determine the emitted light modal radius. Knowing the beam waist, the values of other parameters of the beam can be calculated.

Theoretical models of light scattering methods are considered for precise dielectric surfaces. By use of microscopic treatment it is shown, that polarization of near-surface medium in the presence of roughness differs from that in the volume of medium. Simple theoretical model of near-surface polarization dependence due to effective field difference is presented for the case of s-polarized incident light. Corresponding light scattering is calculated by use of quasi-microscopic approach. It is shown that the intensity of scattering decreases noticeably for very smooth surfaces, which height deviations are compared with interatomic distance (approximately 5 A for SiO₂). Therefore the differences of power spectral density functions measured by angle-resolved scattering and atomic force microscopy methods may be qualitatively explained.