Paper present a review of theoretical study and numerical simulations of effects of nonparaxiality on spatial optical solitons in transparent media with various types of optical nonlinearity: Kerr-law and saturating self-focusing non linearities in isotropic media and second-order nonlinearity in anisotropic media. The main features of spatial solitons, including their stability, transient process, and polarization characteristics are found. Conjunctions for formation of 'optical needles' - spatial solitons with sub- wavelength width - are formulated.

The intrinsic optical bistability, soliton formation, and transient phenomena such as the free polarization decay and photon echo in dense resonant media are investigated, taking into account the short-range dipole-dipole interaction of atoms.

We consider the self-compression of the cnoidal waves of both cn- and dn-types in the materials with focusing Kerr nonlinearity. The dependencies of the compression degree and optimal media length on the parameter describing localization of the wave energy are presented and the main features of the wave propagation are analyzed on the basis of finite number harmonic approximation.

Theoretical and experimental analysis of two schemes for controllable transformation of short laser pulses coherence is presented: self phase-modulation in CCl₄ with thermal nonlinearity and time-delay line. Such methods can be utilized in high-speed schemes of speckle-noise reduction for perspective systems or laser UV projective lithography.

Generation of ultra-short soliton-like pulse from a weak- modulated signal by induced modulational instability is simulated within lossy nonlinear dispersive optical fibers using the beam propogation method. Compression ratios and optimum fiber lengths required to achieve a train of short pulses at the output of the fiber are presented in normalized form.

We study the propagation of electromagnetic waves (EMW) in a dielectric fiber by considering a different type of nonlinearity in the material other than the usual Kerr effect. The nonlinearity is the torque produced due to the rotation of the dipoles in the material by means of an external electric field. We find that the electric field component of the propagating EMW satisfies the derivative Nonlinear Schrodinger equation and hence it propagates in the form of solitons. Also, the dipole dynamics is also in the form of solitons.

The optical soliton train propagation is studied under the action of intra pulse Raman scattering (IRS). It is shown that IRS induces decay of the soliton train at het early stage of this propagation. As a method to suppress the adverse action of IRS, a train propagation in a composite medium with fast and slow relaxing cubic non-linearities is analyzed.

Gaussian's functions are used to investigate properties of light bullets in Kerr non linearities media. It is shown that the light bullets oscillate in space and time. The type of the nonlinearity and the collapse problem is discussed.

We report the optimization of a periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO) pumped by a diode-pumped, Q-switched Nd:YAG laser operated at 1064 nm. Total conversion efficiency exceeding 66 percent was achieved.

Using hydrodynamic model of a semiconductor -plasma and following the coupled-mode approach, an analytical investigation of excitation of a polaron mode is made in a direct gap III-V weakly polar, doped semiconductor in the presence of an applied magnetostatic field. The effect of magnetostatic fields on the basic operational characteristics of a parametric oscillator, viz., threshold condition and conversion efficiency has been critically analyzed. Numerical estimates are made for an n-InSb crystal at 5K duly irradiated by a pulsed 10.6 micrometers CO₂ laser. The results are found to be in a good qualitative agreement with available experimental observations.

A vortical structure of second harmonic (SH) field excited in quadratic nonlinear medium by combined beam composed of two hollow Bessel beams of fundamental frequency is analyzed. An emergence of the pairs of single-charged vortices in SH beam caused by interaction of Bessel vortices is revealed. Experimentally, splitting of frequency-double Bessel vortex of topological charge into 2m single-charged vortices was observed.

It is shown, that influence of self-action effects is capable to expand a spectral range of resonant optical harmonic generation and in three-photon resonant medium with positive dispersion under tight focusing the influence of ac Shtark shift results in fourth-order power dependence of third harmonic efficiency on fundamental intensity and medium density. The comparison with known experimental data is carried out.

We develop theory of the second harmonic generation (SHG) in nonlinear optical crystals with random domain structure. The theory takes into account fluctuations of phase mismatch and nonlinear wave coupling coefficient. Dependence of SH intensity on interaction length and fundamental radiation intensity is examined. The latter may differ from quadratic law in the region of small nonlinear conversion efficiencies.

A new solution of Maxwell equations corresponding to elliptical Bessel beams has been obtained. The polarization of the elliptical light beam and the structure of its Fourier spectrum have been determined and the energy flux has been calculated. Nonlinear polarization has been found and a system of reduced equations for the process of generation of a second harmonic elliptical beam has been obtained.

The scheme for obtaining quadri-beams is studied theoretically and experimentally. In this scheme the quadri- beam is obtained from the plane wave or Gaussian beams using two biprisms. Using optical elements with different number of reflecting planes one can obtain the beams with complex symmetric intensity patterns. The second harmonic generation by quadri-beams is experimentally investigated. The theoretical explanation of the obtained spatial distribution of second harmonic radiation is given.

In this paper we represent the results of investigations of a UV-induced nonlinear absorption in BBO crystals and its influence on frequency conversion. The assumption that in BBO crystal at two-photon absorption of law intensive radiation < 100 MW/cm² at 266 nm dynamic color-centers are generated. With the help of computational modeling it was defined that the absorption cross section of dynamic color-centers at 266 nm is equal to approximately 8 X 10^-17.

We report on spectra of supercontinuum generation in optical fiber pumped by 30 ps pulses of parametric oscillator tunable in the vicinity of zero dispersion point both int normal and anomalous regions. Shape of output spectra strongly depends on detuning and by pumping in anomalous region it extends to 2100 nm.

Raman amplification in barium nitrate crystal is studied using focused laser beams for the different amplification regimes and focusing conditions. The realized method of study allows one to observe the saturation of Raman amplification as a valley in the experimental curve. Also, it is possible to determine Raman gain coefficient using the fitting of the experimental dependences.

We present a new, to our knowledge, method of anti-Stokes generation at stimulated Raman scattering in media with variations of third order nonlinearity along longitudinal coordinate. By numerical simulation the quasi-phase matching condition in different media and achievement of high efficiency of transient anti-Stokes conversion are obtained. The dependence of energy conversion from pump into anti- Stokes wave on the relation of input intensity of pump and Stokes waves is computed. We received the models of media in which the efficiency of anti-Stokes generation exceeded 30 percent. The results of the study can be used for the development of new effective nonlinear-optical devices for laser frequency conversion.

The angular and spectral nature of the emission spectra of sodium atoms driven by the laser tuned near the dispersion- free point of the main doublet has been studied. The experiment shows strong angular dependence of parametrically generated waves. The main features of the registered emission spectra can be explained as a result of FWM in a V- type system. Experimental results show that self- filamentation does not play critical role in forming cone radiation.

In the present work we investigated the conditions of the 4th harmonic stable high effective pulse generation with the energy up to 100 mJ, efficiency approximately 50 percent and pulse repetition rate 10 Hz in DKDP crystals with noncritical phase matching. On the basis of experimental data we carried out the numerical modeling of thermal self- action effects influencing on the efficiency of the 4th harmonic single-shot pulse generation and received the solution of non-stationary heat conduction equation, describing radial temperature profile in crystal as a function of time. It was shown that maximum efficiency of the 4th harmonic generation in the thermal self-actions conditions is reached when initial crystal temperature is less than noncritical phase matching temperature and in the process of heating during the pulse inside the crystal radial temperature profile close to the noncritical phase matching temperature.

The perspective materials for nonlinear optics from the point of view of realization of more various directions of synchronous interactions are biaxial crystals. They have high components of a nonlinear susceptibility, many of them are easy to grow, cut and nonhygroscopic etc. Besides a series of them allow to realize simultaneously some types of nonlinear interactions of light waves. It allows to use them as elements of optical memory, nonlinear optical logic elements of computers, in devices for visualization of IR radiation.

The experimental results of an investigation of the self- action of Bessel beam propagating in the benzene are presented. The typical modifications of the far-field intensity distribution of Bessel beam caused by its self- action are revealed. A good agreement with computer simulation results is obtained.

We have investigated the influence of cubic optical non- linearity and derivative of group velocity on laser beam divergence by the propagation in 1D photonic crysatl which is layered periodic structure formed by anisotropic media. It has been established that the laser beam divergence is determined by two physical mechanisms: influence of non- linearity and scattering gon diffractional grating appearing in the crysatl because the presence of periodiciity of optical properties. It has been shown that the second mechanism may become the reason of strengthening the focus. We have analyzed the influence of low-frequency electric field on this phenomenon. It has been found the conditions of non-diffractional beam propagation in photonic nonlinear crystal.

In this communication we present a study regarding the limitations that geometry imposes on the degree of phase matching attainable in a self-diffraction experiment. We find that to generate a strong signal the effective area over which the incident beam are superposed within the nonlinear medium must contain spatial variations on a length scale equal to the inverse of the phase mismatch. We develop a simple model that allows us to interpret the generated signal in terms of a sum over contributing phasors from each plane of constant phase within the active region. The phasors tend to add together to create a spiral figure reminiscent of Cornu Spirals in diffraction theory.

The nonlinear optical properties of sodium di-2- ethylhexysulfosuccinate (AOT)-water-isooctane microemulsions are studied as a function of reverse micelluar size. Extremely large nonlinear optical effects are observed far away from the critical temperature for phase transitions. We propose that this is due to a combination of electro- strictive and thermo-diffuse effects.

There are presented results of theoretical investigation of nonlinear self-depolarization effect resulting in variation of space distribution of polarization-ellipse parameters of high-intensity focused laser beam. In particular, both linear and circular initial polarizations are shown to change and turn into elliptic polarization with inhomogeneous distribution of polarization-ellipse parameters in focal area. Detailed results and calculations are presented for particular case of Gaussian beams of low order. Bearing in mind obtained results, we discuss specific symmetry structure of self-depolarization effect allowing experimental checking of described phenomenon. There are analyzed and estimated other contributions to depolarization effect resulting from low-intensity diffraction. Possibility of observing polarization dependence for damage and self- focusing threshold in transparent materials is also considered.

The self-channeling of cylindrical light beams versus the excitation density, light frequency, and crystallographic orientation is numerically analyzed in GaAs, ZnSe, CdS semiconductors. A comparison of the data obtained and reported for diode and streamer semiconductor lasers is made. Made out of reversing of the angular anisotropy of the real third order nonlinear optical susceptibility is worthy to be studied for a practical implementation.

Self-diffraction of Bessel light bema in heavily doped n-InP has been experimentally studied. It is found that additional rings which have double structure appear in spatial spectrum of diffracted light. At certain conditions Gaussian like central maximum can be also observed in spatial spectrum. Numerical simulations have been performed for the case of Raman-Nath regime and saturation nonlinearity. The results of simulations are in a good agreement with experimental data. The double structure of the diffraction rings can be explained in terms of the existence of forbidden directions for light diffraction.

The aero-optical problem of laser beam propagation through a contrail is solved by using a rigorous numerical calculation of the nonlinear Schrodinger equation and an asymptotic description of a turbulent condensation trail behind a large civil aircraft, including particle sizes distribution of the polydispersive water aerosols.

A variety of novel materials has been synthesized including poly(ethynediyl-arylene-ethynediyl-silylene)s (PEAES) containing hypercoordinate silicon, and films of metal- containing polyacrylonitrile materials. The (chi) ⁽³) properties in various matrices have been investigated by various techniques such as DFWM and Z-scan. The (chi) ⁽³) values are outstandingly high; e.g. sol-gel films incorporating 5-14 mass percent PEAES show Re(chi) ⁽³) equals 3-9 X 10^-11 esu, and films of Cr-containing polyacrylonitrile materials synthesized by the polycyanoethylation reaction between acrylonitrile and Ar₂Cr show (chi) ⁽³) equals -2.5 X 10^-10 esu.

A considerable number of new crystalline compounds were prepared by reacting L-arginine (L-Arg) with a series of inorganic and organic acids. In addition to the usual arginine slats with composition L-Arg-HX, where HX represents various acids, an entirely new class of crystal with the composition L-Arg 2HX was discovered. Due to the presence of the optically active L-arginine component, all these crystal had non-centro-symmetric structures. Most of the crystal prepared in this study gave strong phase-matched second harmonic generation signals with a Nd:YAG laser, and some appear quite promising for nonlinear optical applications.

Crystals of para-nitroaniline were grown from solution while subjected to a strong dc electric field of 2 X 10⁵ V/m. This resulted in a modification of the unit cell lattice parameters and space group with respect to crystal grown in the absence of an electric field. The modified crystal are capable of generating a second harmonic signal and poses a significantly lower dielectric permittivity.

The accounted by us in dislocational model a room-temperature photorefractive effect [1] due to failure of dislocations to new fastening points [2]. It gives to initiation of electrical polarized areas in light heating zones in KDP crystal. In this investigation pulse currents generated in the crystal at its pulsing irradiation have been detected.

A forming optical contortion in a crystal undoped lithium niobate at transmitted laser emission researched by the method of monitoring of second harmonic generation kinetics. The basic changing of refraction index is combined with a transport charge processes for the phase matched second harmonic generation, and with a local recharge effects of photorefractive centers for the phase mismatched generation. The external magnetic field changes a photorefractive sensitivity of a crysatl. They are compensated photorefractive sensitivity up to 0 in the magnetic induced field -0.38 T. The influence of a magnetic field is concerned with changing conditions of an electrons photoexcitation.

Defects in nonlinear optical barium metaborate crystals have been investigated by means of optical spectroscopy and thermally activational methods. Low-temperature absorption peaks have been observed at all samples. The dependence of these peaks upon crystalline phase and type of the flux used while growing is low. This fact indicates that intrinsic defects play the leading role in absorption origination. It is shown that while growing BBO crystals by TSSG technique, defects, which form deep electron-type traps in the forbidden gap, are generated.

Ba_0.77Ca_0.23TiO₃ (BCT) crystals have interesting photorefractive and electro optic properties as was recently demonstrated by several papers. Analyzing these results and our own experiments we have got the conclusion that there is an effective bulk electric field inside the crystals. In order to estimate the value of the suggested field inside the crystal we have developed an experimental method based on two- and four-wave mixings presented in this paper, whereas we are using a BCT crystal that has been grown by Ch. Kuper and co-workers from the University of Osnabrueck. Knowing the value of the bulk field we have estimated the value of the effective photoconductivity of the crystal.

Thin films of molecular aggregates of pseudoisocyanine were obtained. Delocalization length of exciton wave function was measured with an assumption that an absorption line width is defined by disorder induced mixing of the lowest states of the one-exciton band. Predicted effect of size enhancement of the nonlinear optical properties for molecular aggregates was observed. The assumption used to determine the delocalization length is shown to coincide with the observed optical nonlinearity size enhancement phenomenon.

In the paraxial limit the photorefractive response of a cubic gyrotropic crystal with applied square-wave electric field is considered for the symmetric incidence on a crystal of two plane light waves with approximately equal intensity. The theoretical description is based on the nonlinear equation for the time-average value of the space-charge field and coupled-wave equations for the amplitudes of the eigen waves of a crystal. It takes into account the additional light waves diffracted int eh second orders. The numerical modeling of the self-consistent interaction in B₁₂TiO₂₀ crystal is made for the diagonal electro-optic configuration of interaction.

For nonlinear optical materials in which the excitation diffuses significantly during the time scale of measurement the usual analysis of a Z-scan experiment must be modified. We develop a simple first order theory based on a quadratic rather than Gaussian spatial modulation of the index of refraction. This leads to asymmetric Z-scan curves. We apply this theory to the study of the thermal-optic effect in a simple neutral density filter. A significant spatial phase chirp can be induced in these filters at modest intensities. The observed transmission curves agree well with the quadratic theory.

We report polarization dependent measurements of absorptance of some crystal performed according to the ISO11551 standard by the 'pulse' or 'gradient' calorimetric method at 1064 and 532 nm using a pulsed, diode-pumped, Q-switched YAG:Nd laser.

The interaction of a nematic liquid crystal (NLC) with the succession of the femtosecond light pulses has been investigated. Direct experimental comparison between the nonlinear NLC response to femtosecond and cw radiation was performed.

On the basis of study of the optical properties and IR- spectra of nonlinear polymeric waveguides it is concluded that there is a preferred orientation of the azo-dye molecules in a rigid polymeric matrix.

Nonlinear optical properties of semiconductor and dielectric thin films are studied at a wavelength of 632.8 nm in the range of light intensity below 0.1 W/cm² by the method of the spatial Fourier-spectroscopy of guided modes. The nonlinear refractive index and the absorption coefficient were found to be about 10^-3 cm²/W for semiconductor films and multilayer structures and about 10^-6/W for quartz glass films. Origin of this optical nonlinearity is considered as the modification of surface states in the band gap. New approach of the low- dimension structure investigation and new method of determination of a nanolayer thickness are considered. The method is based on recording of transformations of the angular Fourier-spectrum of the reflected light beam int eh self-effect case during gradually increasing of the incident light beam intensity up to 0.1 W/cm² with excitation guided mode in thin-film structure.

The photophysical and nonlinear properties of some push-pull fluorinated 4-(dicyanomethylene)- pyranes using the steady- sate and time-resolved picosecond spectroscopies with an electric-field-induced second-harmonic-generation technique have been investigated. Strong fluorescence quenching and large shifts of time-resolved transient picosecond spectra on going form nonpolar to polar solvents are connected with effective charge transfer interactions of polar singlet excited molecules with a polar environment. The high second- order polarizabilty (beta) equals 260 X 10^-30 esu for one of the investigated push-pull pyranes allows to propose using such kind of molecules in the development of second- harmonic-generation elements.

Absorption saturation as well as bleaching relaxation of ⁴A₂ yields ⁴T₁(⁴F) transition of tetrahedrally coordinates Co2+ ion in magnesium-aluminum and magnesium-gallium-aluminum glass ceramics prepared under different conditions were studied. Ground state absorption cross sections at the wavelength of 1.54 mm were estimated. The level of unsaturable losses was observed to be proportional to the cobalt concentration in the raw materials. The difference spectrum of stimulated emission and excited state absorption under excitation in the ⁴A₂ yields ⁴T₁ (⁴P) transition of the tetrahedral Co ion was derived and analyzed.

Group representation of wave equations of crystal optics is developed. On this base the new solution and the simple expressions of propagation velocities and refractive indexes of optical radiation waves in dielectrics are obtained. 2D representation and particularity in gyrotropic crystal are considered. Obtained expressions are used for applied nonlinear optics. Simple expressions of direction three-wave phase-matching cones in biaxial crystals are deduced.

We consider switching characteristics of the nonlinear unidirectional coupler embedded in the photorefractive medium with purely diffusion nonlinearity. Transmission characteristics for both two- and three-waveguide couplers are presented. It is shown that the part of energy transmitted into the second waveguide in two-waveguide coupler monotonically decreases with increase of input energy i.e. no threshold energy value exists. It is also shown that due to the specific character of diffusion nonlinearity transmission characteristics of the three- waveguide coupler strongly depends on the relative disposition of the input waveguide.

It is shown that crystalline quartz which is placed inside the telescope and whose optical axis is parallel to the beam axis may decrease the depolarization of radiation caused by thermally induced birefringence in the Faraday isolator. The isolation ratio has been increased by a factor of 8 in experiment.

Barium nitrate crystal are studied using one- and two-beam Z-scan techniques by excitation with the second harmonic radiation of nanosecond Nd:YAG laser and probing with the cw He:Ne laser. For the first time, a thermal lens due to the dissipation of energy of the SRS-excited A_g vibrational mode to the heat is observed and measured.

Investigation of nonlinear interferometers symmetrically pumped by two light beams has been proposed. An analysis of the conditions for realization of symmetrical and asymmetrical optical bistability, different spatial-temporal structures due to symmetry breaking bifurcation has been performed.

Optical pattern formation is studied far beyond threshold in a single-mirror feedback scheme using sodium vapor as the nonlinear medium. Patterns with twelve fundamental wave vectors arise form hexagons in a secondary bifurcation. Besides irregular patterns, quasi patterns and superlattices are obtained. Even after a tertiary bifurcation the patterns remain stationary. Fourier filtering experiments show that the harmonics of the fundamental wave vectors are essential for the stability of the secondary and tertiary patterns. A novel Fourier filtering technique is used for a measurement of the neutral stability curve and proves experimentally the existence of multiple instability regions existing due to the periodicity of the Talbot effect.

We present the preliminary results of investigations of influence of the finiteness of device aperture, axial magnetic field and external feedback mirror on the transverse structure of emission of a broad-area VCSEL. We use the model developed in our recent works which takes into account the spatially dependent reflection from DBR mirrors of a VCSEL. It is shown that boundary conditions can freeze a temporal dynamics of long wavelength instabilities which are presented in an unbounded device. The external feedback changes relative threshold of polarized spatial Fourier modes. A presence of axial magnetic field only slightly increases polarization degree of patterns arising near the laser threshold.

A new theoretical model of SRS for a Bessel pump beam is presented. The experimentally observed regularities of SRS, concerning the formation of output patterns an nearly diffraction-limited axial Stokes beam are explained within the framework of this model. The model represents the Stokes radiation as a superposition of partial Bessel modes if a cylindrical waveguide is formed by a pump beam.

Multiple images formation after propagation of periodical wave field over a fraction of Talbot distance (Zr) was received explicitly. The phase-locking of multi core fiber laser radiation was achieved experimentally by usage sector mirror placed at a distance of Zr/8.

Stochastic interference fields are obtained when measuring light wave interacts with a partially scattering surface has to be investigated. The resulting interference fringe pattern ca be evaluated optimally on the basis of the stochastic filtering approach. Discrete Kalman filtering procedure was applied to 2D fringe pattern evaluation. It was developed the first order nonlinear 2D Kalman filtering method to estimate the phase and fringe frequency of stochastic interference fields. Discrete nonlinear Kalman filtering method generally provides the optimal fringe pattern estimates. The accuracy and noise-immunity of 2D nonlinear stochastic Kalman filtering were verified. Developed recurrence processing procedure was realized experimentally with application to 2D noisy fringe pattern analysis.

Results of theoretical consideration of polarization dynamics both with steady states and their stability in a single mode laser with stimulated anisotropy in a saturable are proposed. Examples of coexistence of stable steady states with two linear orthogonal polarizations are given. Dynamical regimes with different types of limit cycles with linear and elliptical polarization are demonstrated.

Spontaneous pulsations of intensities, continuous change of instantaneous phase difference between counterrunning waves on π at transition from negative to positive tunings while their mean phase difference remains unaltered as well as jumps on 2π of mean phase differences were found in a four-frequency ring gas class-A laser with elliptically polarized eigenstates in the presence oflinear coupling.

Spontaneous pulsations of intensities, continuous change of instantaneous phase difference between counterrunning waves on (pi) transition from negative to positive tuning while their mean phase difference remains unaltered as well as jumps on 2(pi) mean phase differences were found in a four- frequency ring gas class-A laser with elliptically polarized eigenstates in the presence of linear coupling.

This work presents the results of an experimental study of the self-modulation regimes in a ring CO₂ laser with a nonplanar cavity that makes it possible to remove radiation polarization degeneracy and realize a four-wave regime of generation. Such a regime enables one to investigate the dynamics of interaction of four waves with elliptical orthogonal polarization under the conditions of a class B laser with a quasi-homogeneous character of amplification line broadening.

Investigation and modeling of dynamics and stability of long-wavelength quantum-well lasers with carrier transport effects subject to a phase-conjugate mirror has been developed. Unremovable in quantum-well lasers carrier transport affects significantly both cw and dynamic laser performance. Laser stability, phase locking, and dynamics have been studied by the analysis of the laser rate equations describing optical field and carrier transport including carrier diffusion is separate confinement heterostructures, carrier capture and escape in quantum wells. It has been shown, that in long-wavelength quantum- well lasers carrier transport narrows drastically the laser- stability reign in approximately equals 1.5 to approximately equals 2.5 times and increases the unstable -output oscillation frequency in approximately equals 2 to approximately equals 3 times.

We present a theoretical study of the influence of the direct coupling of the average lattice strains to the active ions on the behavior of a Cr³⁺:LiSAF gain switching laser. It is found that the resulting nonlinear time- dependent lensing effect combined with an internal hard aperture behaves as a saturable absorber. A resulting self- Q-switching is observed from the calculated laser pulses.

We have performed a theoretical analysis of conditions of existence and stability of coupled dissipative solitons in an interferometer with a threshold-type of nonlinearity driven by external coherent radiation. For two-soliton structures we demonstrate splitting of spectrum of soliton width. For periodic structures of solitons we found zonal spectrum of characteristics. We studied analytically effect of small- and large-scale inhomogeneities of characteristics of the driven radiation and optical cavity on main features of dissipative optical solitons.

In this paper we report the new two-loop feedback stabilization system allowing stable operation of both continuous and pulse lasers in wide range of active media gain and resonator Q. Different combinations of negative and positive feedback loops were investigated. Negative one round-trip time T_r delayed and positive 2T_r delayed feedback loops combination was found to provide the extremely large stability zone. In self-mode-locked laser, such combination leads to the significant laser pulse shortening.

The scenario for stability loss of laser solitons is analyzed. The process of radial symmetry breaking and bistability between symmetrical and rotating solitons is demonstrated. New, rotating and oscillating soliton state is founded. The consequent period-doubling of symmetrical oscillations is found as a route to chaotic behavior.

Novel mechanisms resulting in generation bistability of passive mode-locked lasers is predicted. It is shown by numerical simulation that after transient evolution either stationary single pulse operation or operation in which the whole laser cavity is filled with the generated radiation can be realized depending on the initial conditions. This bistability is connected with the phase-modulation instability of passive mode-locking in circumstances where the spectral gain-loss profile has a complicated from. The complicated profile can be related to a spectral selectivity of parasitic losses or to a spectral selectivity of parasitic losses or to a spectral inhomogeneity of an active medium amplification. The assumed manifestations of this mechanism in actual experimental systems are discussed.

Synchronization of chaotic lasing in a system master and slave oscillators each consists of two diode lasers is studied numerically. Possibility to extract information signal modulation transmitter output from slave laser output is evaluated.

We present the results of numerical simulation of a nonlinear optical system with a time-delayed feedback which exhibits spatio-temporal chaotic states. The model incldues three main phenomena governing the system: temporal delay, diffusion and diffraction. We focused our attention on the statistical properties of this system and analyzed the join action of mentioned phenomena, features of spatial spectra in wide range of parameters, scaling relations. We found that under certain conditions powers spectrum of phase fluctuations in chaotic states monotonically decreases as a function of spatial frequency. This causes us to anticipate that such class of optical system can be used for an artificial optical turbulence simulation.

The suppression of chaos in a laser diode with an external optical feedback is analyzed and experimental results are presented. The intensity noise suppression and the emission line reduction by a small perturbation in the laser current are shown. This technique can be applied as a low cost replacement for an optical isolator in spectroscopy, interferometry and other areas.

The stochastic resonance (SR) in a fast threshold electronic light emitting system is studied. The measurements were carried out on the frequency 18 kHz high than in other electronic systems. We have registered the phenomenon of a SR, which is displayed in the nonmonotone behavior of the dependence of optical response of the system at the simultaneous action of the signal and the noise, when the external noise is being changed. It is suggested that it can be possible to describe the SR in such threshold systems as lasers, in terms of phase transitions.

We present an experimental study of the Yb-doped double-clad fiber laser operating in the 1.08 micrometers wavelength. The fiber side-pumped with a high power laser diode using the v- groove technique. Various experimental configurations are performed from the linear cavity to an all-fiber tunable unidirectional ring cavity. Mode-locking of the Yb laser are investigated using the nonlinear polarization rotation.

The response of a single mode semiconductor laser to an injected external signal has been studied. The control parameters are the power and the frequency of the injected signal together with the gain of the laser. The injected power varies from 6 down to -120 dBm. Following the magnitude of these control parameters many phenomena can be observed. When both injected field and laser eigenfield are of the same order of magnitude they compete in a non-linear way, leading to frequency generation, push-pull effects, hysteresis phenomena and chaos. For weak dBm the laser behaves with the injected field in the same way as it does for the spontaneous emission which is its natural source. We describe the role of the injected laser as a filter and an amplifier in this case. It follows that the laser can be used to process information in ways that are not yet completely exploited.

We study the effects of spatial coupling in the noise properties of microchip lasers. We demonstrate that the synchronization phenomena commonly observed in spatially coupled unstable laser applies to the quantum-noise-driven dynamics in steady-state stable laser; this allows us to predict a new method of the generation of twin laser beams. We derive simple analytical expressions for the synchronization-induced noise reduction phenomena. We observe a compete suppression of the dominant relaxation oscillations peaks in the intensity difference noise spectrum, as well as photon statistics approaching the standard quantum limit.

ZnSe/ZnMgSSe and InGaN/GaN heterostructure based lasers under optical transverse pumping by pulsed N₂-laser radiation were investigated in a wide spectral, temperature and excitation intensity range for various types of heterostructures which differed in the epitaxial layer composition, layer sequence and thickness. The spectral- angular distribution of the laser emission of the ZnSe/ZnMgSSe separate confinement heterostructures and the influence of the excitaion intensity and the cavity length on the laser mode structure were investigated. It was found that the main degradation mechanism of the ZnSe/ZnMgSSe multiple quantum well heterostructures at temperatures higher than 400 K is the diffusion of S atoms from the barriers into the quantum wells which leads to increasing point defect concentration in the active layers of the laser. The recovery of the laser threshold of the ZnSe/ZnMgSSe MQW-SCHs degraded during thermal annealing after the action of the inherent laser radiation is attributed to a significant decrease of the point defects in the active layers. Laser action of InGaN/GaN multiple quantum well heterostructures in the blue spectral region has been obtained for the first time and investigated. Temperature tuning of InGaN/GaN MQW laser emission from the violet to blue has been realized. The influence of the photoluminescence characteristics on the laser parameters of the InGaN/GaN MQW optically pumped lasers operating in the blue spectral region is investigated.

A decrease in the depolarization ratio by more than an order of magnitude using a recently proposed Faraday mirror in comparison with the traditional Faraday mirror has been demonstrated in experiment. At a high average laser power, the possibility of increasing the accuracy of compensation of depolarization in the active element by means of a (lambda) /4 plate using both the traditional and the novel Faraday mirror is shown.

The possibilities of realizing an intracavity self injection regime in laser with short-term resonant modulation of losses (STRML) have been investigated. It is shown by calculations, analytically and experiments that natural chirp is proposer to USP of the STRML-laser. The monoblock construction of electrooptical double modulator for the STRML-laser has been represented.

Design of novel integrated structure-semiconductor broadband saturable-absorber dispersion controlled mirrors for mid IR spectral range lasers have bene discussed. The novel design of SESAM is based on the multilayer structure like Gires- Tournios interferometer. High reflector consists of the metal mirror with low losses in this spectral range. Top section consists a few layers forming the linear grown dependence of group delay by resonance effects of interferometer. The thin HgCdTe quantum well layer with nonlinear absorption can be included in transparent semiconductor layer near the antinode of standing wave. This structure has low amounts of nonequal thickness layers that create the high reproducibility way of such type structure experimental realization. SESAM design for Cr:ZnSe laser is analyzed in detail.

Results of numerical investigation of transversal cavity mode influence on static and dynamic characteristics of oxide-confined vertical-cavity surface emitting laser are presented and discussed. It was shown that mode selection could improve modulation properties of laser. Instigated the influence of injection current on near field distribution and spatial hole burning effect.

Stationary characteristics and relative intensity noise are simulated for a laser diode with strong filtered optical feedback from an external Bragg reflector. Multiple reflections in external cavity are taken into account through the introduction of Green functions. An analysis of the stationary solutions shows the appearance of new solutions for strong feedback and collapse in the plane frequency-gain of the ellipse which usually contains the modes and so-called antimodes. Numerical result are compared with analytical expressions.

The theoretical investigations of diffraction of light beams on phase sinusoidal diffraction gratin placed between parallel mirrors of a Fabry-Perot interferometer are carried out. The problem is solved on the basis of Maxwell equations in the approximation of plane waves. The numerical analysis indicates that the power of beam incident on interferometer with a built-in diffraction gratin undergoes strong redistribution between diffraction orders depending on such parameters as angle of incidence, initial detuning for the interference maximum and index of phase modulation. This feature provides the opportunity to use such grating- interferometer as an amplitude-phase modulator and a spatial switch of a new type. If non-linear optical media are used as an intermediate layer and grating is formed by interferencing light beams, then the parameters of such a modulator can be changed and controlled optically.

The coupling of an external cavity to a laser induces effects that are generally modeled by a plane wave treatment, even though laser optics is rather based on beams having a finite lateral extent. We demonstrate that a Fabry- Perot interferometer acts like an apertured mirror in the sense that its reflectivity can be higher for the TEM₀₀ mode than for the TEM₀₁ mode. We consider the single- frequency and multi-frequency cases.

We propose a new method for transforming an elliptic Gaussian beam, in the near-field, into a circular Gaussian beam in the far field using a very simple diffractive optical element which is a phase slit. We show that a circular Gaussian beam can be transformed into a flat-top profile, a doughnut profile or a ring-shaped profile.