The conversion of the complex salt of TCNQ and triethylamine; TEA(TCNQ)₂ into the zwitterionic NLO chromophore DEMI can be achieved in a polymeric guest host system. Synthesis of the chromophore in a thin polymer film can be monitored by observation of the SHG in an in-situ poling experiment. We discuss the characterization of the conversion process, which could potentially lead to the "writing" of very small areas of nonlinearly active material into otherwise inactive polymer films. We have found that the transformation from organic salt to NLO (Non linear Optical) chromophore occurs at approximately 160°C, the transformation is accompanied by a dramatic change in colour from green to blue and by an accompanying decrease in conductivity. The resultant blue spectrum is identical to that obtained by doping DEMI into PMMA. All characteristic TCNQ^- peaks in the UV/Vis absorption spectrum are completely diminished, and the reaction appears to be almost 100% efficient. In-situ corona poling experiments, while heating a thin film of TEA(TCNQ)₂ in PMMA above its glass transition temperature reveal no SHG from an input wavelength of 1.9 microns until the conversion temperature is achieved. At this point when DEMI has been "synthesised" in the sample the SHG can be observed and its relative intensity measured relative to that of a quartz plate. We also discuss the attempted synthesis in situ of a related zwitterionic NLO chromophore Me-P3CNQ.

Stationary and transient behaviour of photorefractive multiple quantum well structure illuminated by interfering plane waves of near resonant frequency was investigated in frames of photogeneration, diffusion, drift and trapping (PDDT) model. The influence of high intensity electric field applied along the quantum wells planes was considered and an effect of a nonlinear transport of electrons, characteristic for GaAs/AlGaAs samples, was included. An analytical expression for the fundamental amplitude of space-charge field in the sample and the dependence of the photorefractive grating response time on material parameters in the case of low interference pattern contrast is presented and compared with the earlier results.

In this paper we treat two and three dimensional light bullets by somewhat different methods. In both cases stability is achieved for some parameters. In the first case we propose a scheme for stabilizing spatiotemporal solitons (STS) in media with cubic self-focusing nonlinearity and "dispersion management", i.e., a layered structure inducing periodically alternating normal and anomalous group-velocity dispersion . We develop a variational approximation for the STS, and verify results by direct simulations. A stability region for the 2D (two-dimensional) STS is identified. A new stable object, in the form of a periodically oscillating bound state of two subpulses, is also found. We go on to also demonstrate a possibility to stabilize fully three-dimensional spatiotemporal solitons ("light bullets") in the same self-focusing Kerr media by means of a combination of dispersion management in the longitudinal direction and periodic modulation of the refractive index in one of the transverse directions. Assuming the usual model based on the paraxial nonlinear Schrodinger equation for the local amplitude of the electromagnetic field, the analysis relies upon the variational approximation. A predicted stability area is identified in the model's parameter space.

The properties of a novel type of dislocations, called spatio-temporal vortices, are discussed. We propose to registrate them making dynamic interferogram of signal waves. Methods of their generation are suggested as well. It is illustrated that a spatio-temporal dislocation appears due to interaction of two Gauss-Laguerre pulsed beams with half-Pi phase shift. We show that superposition of two non-complanar phase modulated beams gives birth to the train of spatio-temporal vortices, which are periodical in space or time. The dynamics of a spatio-temporal vortex-soliton in defocusing Kerr-like medium is considered.

We have investigated the nonlinear amplitude vector equation governing the evolution of optical pulses in optical and UV region. We have normalized this equation for the case of different transverse and longitudinal size of the optical pulses (long pulses), and also for the case of equal transverse and longitudinal size (so called light bullets or LB). This gives us the possibility to reduce the amplitude equation to several kinds of linear and nonlinear evolution equations in the partial cases. One unexpected new result is the relatively stability of LB and the significant decreasing of the diffraction enlargement in respect to the case of long pulses in linear regime of propagation. In the second part of the paper we look for media parameters and characteristics of the LB to obtain conditions for strong negative dispersion and nonlinearity higher but near to critical for self-focusing. We found that the propagation of LB in these special cases is governed by the 3D+1 vector nonlinear Schrodinger equation (VNSE). For the VNSE exact vortex solutions are found. Conditions for experimental observations of these vortices are determined.

Formation of spatial cavity solitons upon degenerate two-wave mixing in interferometers with Kerr-like nonlinearity has been investigated by means of theoretical and numerical modelling. The process of spatial solitons formation is discussed from investigation of properties of domain walls connecting different intensity levels in the light beams transverse profiles. It has been shown that the spectrum of coupled bright and dark cavity solitons has a zone structure and the transitions between different levels have been studied by means of stability analysis and numerical modelling. An analytical model describing the properties of domain walls connecting different homogeneous solutions were developed based on parametrically driven Ginsburg-Landau equation for complex order parameter. Numerical modelling of multistable bright and dark cavity soliton excitations and their metastable clusters is also performed.

Five-wave spatial Bragg solitary waves in the form of weakly coupled states, occurring with a four-order non-collinear scattering of light by acoustic wave in an optically anisotropic crystal, are recognized. An exact analytical description, including the localization conditions for multi-pulse states, is developed for these solitary waves. Additionally, we elaborate an approach to searching for the spatially localized states with so-called intermediate regime of light scattering. Spatial-frequency distributions for the optical components of multi-pulse coupled states are studied.

We review our recent works on spatial solitons in nonlocal nonlinear media. In particular, we discuss stabilization of two dimensional bright solitons and vortex ring solitons as well as interaction of dark solitons.

Nonlocal nonlinear Schroedinger-type equation is derived as a model to describe paraxial light propagation in nonlinear media with different 'degrees' of nonlocality. High frequency limit of this equation is studied under specific assumptions of Cole-Cole dispersion law and a slow dependence along propagating direction. Phase equations are integrable and they correspond to dispersionless limit of Veselov-Novikov hierarchy. Analysis of compatibility among intensity law (dependence of intensity on the refractive index) and high frequency limit of Poynting vector conservation law reveals the existence of singular wavefronts. It is shown that beams features depend critically on the orientation properties of quasiconformal mappings of the plane. Another class of wavefronts, whatever is intensity law, is provided by harmonic minimal surfaces. Illustrative example is given by helicoid surface. Compatibility with first and third degree nonlocal perturbations and explicit solutions are also discussed.

Ultrashort dissipative optical solitons, originating in single-mode erbium-doped fiber amplifiers are analytically investigated. This type of optical solitons can be grown due to resculpturing external optical pulses by fiber amplifier in the traveling-wave regime. We consider the well-known classical model related to the most desirable practically fundamental solitons and, in so doing, develop extremely extended analytical approach including the application of the consistency equation. The consideration performed is related to the regimes without and with the gain saturation in a doped fiber and demonstrates that these fiber amplifiers can form and support in this regime various dissipative optical solitons in the form of dark and bright solitons as well as the shock waves. For all the regimes, the amplitude and frequency distributions are estimated.

We have measured the photovoltaic current of the iron doped lithium niobate and determined the photovoltaic constants of the photovoltaic tensor. We used 0.25 wt.% Fe (verified with Rutherford back scattering method) doped z-cut crystals. We used the coplanar surface electrodes setup. The current was measured by a picoampermeter. We have analyzed the current as a function of the optical intensity and as a function of the polarization angle of the laser beam. The accuracy of the measurements is estimated to be of about 20%. We used the measured photovoltaic effect for the generation of spatial solitons. We generated dark planar photovoltaic spatial solitons in iron doped lithium niobate, and we measured properties of the waveguides generated by the spatial soliton. We created dark photovoltiac solitons in a bulk crystal with the optical intesity 1-10 mW/cm², and the soliton's FWHM about 5-18μm. We observed the temporal evolution of the one-dimensional dark photovoltaic solitons under open-circuit condition, and the self-defocusing effect of the laser beam. The steady-state measurement (stable soliton) was obtained after a 6-15 min exposure. For the generation the argon ion laser beam at the wavelength of 514 nm was used. It was polarized along the optical axis and collimated to a diameter of about 2 mm on the input face. The resulting index perturbation forms a planar waveguide. We have measured its properties-the refractive index change and attenuation of the TE mode at the red He-Ne laser wavelength of 632.8 nm.

In this work we investigate light beam propagation in twisted nematic liquid crystalline film. In the linear case (for low power of the light beam) the diffraction and walk-off of the light beam is observed. Due to the optical reorientation nonlinearity light beam is self-focusing and finally spatial solitary wave is created. The direction of light beam propagation is also changing with increasing the nonlinear effect. The samples were filled with 6CHBT nematic liquid crystals and we measured the propagation of light beam at the distance of few millimeters. Nonlinear self-focusing was observed for a light power of order of few tenths of milliwats. The experimental results are in a good agreement with theoretical predictions and numerical simulation. The proposed configuration of our cell can be applied to switching of the light beam in low power all-optical systems.

Phase conjugation are optical devices that can generate a time-reversed replica of an incident electromagnetic wave. These devices play an important role in many optical system that require the transmission of optical waves through scattering media such as the atmosphere. Here we present four wave mixing configuration as one of the most important methods of generation and explanation of process of generation phase conjugation light the coupled equation was solved by three methods: undepleted pump approximation exact solution and two wave mixing approximation. Although exact solutions can be derived for four-wave mixing, the results are difficult to use because of the complicated transcendental equation involved. Solved the coupled equations and introduce an approximation in which two-wave mixing is the dominant process. In this approximation, we assume that the grating is dominated by a pair of waves. A comparative study of the diffraction efficiency as a function of fringe spacing, of some commonly used ferroelectric, non-ferroelectric crystals is presented.

An influence of electrons diffusion on the intensities of switching for absorption optical bistability based on high-intensity femtosecond laser pulse interaction with semiconductor is studied. The dependence of absorption coefficient on free electrons concentration and on induced electric field strength or its potential is considered. With the help of computer simulation an anomalous influence of electrons diffusion on intensities of switching under taking into account of free electrons mobility.

Anderson localization in linear and weak nonlinear 1-D photonic crystal (PC) is considered. An influence of PC layers length fluctuations on nonlinear localization is also under consideration. The nonlinear light localization takes place due to self-formation of ultra-short high-intensity solitons, which reflect from boundaries between the linear and nonlinear layers as whole if nonlinear PC layers alternate with the linear ones. The variation (up to 20 %) of PC layer's length doesn't change the nonlinear localization process essentially. It results in increasing of input pulse intensity for which localization takes place. This aspect is very important for observing of it in physical experiment. In contrast to Anderson localization, the nonlinear one takes place not only in PC with big number of layers, but in a few-periodical structures too. The strong variation can either increase the quantity of initial pulse energy localized in PC, either damp the localization at all under the condition of unvaried intensity of input pulse.

The combination of photonic crystals and nonlinearities is the subject of intense research. Because of the strong dispersion and localization effects in band gap structures, even weak nonlinearities can be exploited. The inclusion of the Kerr effect gives rise to nonlinear energy localization. In combination with the discrete nature of the photonic crystals this may lead to nonlinear modes, such as gap solitons or discrete breathers. We examine a novel kind of solitary wave. The used geometry is a photonic crystal formed by a square lattice of rods containing a Kerr type material: in the linear case a wave with frequency within the band gap is exponentially dampened. However, in the nonlinear regime, the wave creates its own waveguide channel, by changing the indices of the center rods. In the transversal direction with respect to the propagation, the mode is still confined. By applying a Green's function method limited to a photonic crystal strip perpendicular to the propagation direction, we have been able to describe these Bloch modes. To that end, we review a nonlinear lattice model that includes the long-range rod-to-rod interaction between the scattered fields and the non-local nonlinear response of the photonic crystal. The advantages of this semi- analytical approach are discussed and a comparison with a rigorous numerical analysis is given.

A brief overview of recent theoretical results concerning the existence and stability of three-dimensional solitons in self-focusing media with imprinted two-dimensional harmonic or radially symmetric Bessel optical lattices is given. It is concluded that such photonic lattices support one-parameter families of three-dimensional solitons, which are stable within one interval of the values of their energy (for harmonic lattices) or even within two intervals of the values of their energy (for Bessel lattices), provided that the lattice strength exceeds a threshold value. The Hamiltonian versus soliton norm has two or even three cuspidal points (a "swalowtail"-like bifurcation pattern, which rarely occurs in physical models). The results suggest new approaches of making stable spatiotemporal optical solitons ("light bullets") and three-dimensional solitons in attractive Bose-Einstein condensates.

We investigate nonlinear propagation of light in 1D array of optically induced waveguides. The array is generated by two plane waves interfering in slab waveguide core made of photorefractive material with a quadratic electrooptic effect. The influence of the guided wave on the refractive index distribution of the array and the possibility of discrete solitons generation is considered.

We discuss Bloch oscillations in waveguide arrays created in a nematic liquid crystalline layer. Bloch oscillations can originate from the specific distribution of refractive index, where a linear gradient is added to the transverse periodicity. Light can oscillate periodically in the transverse direction as it propagates, returning to its initial spatial position and profile after each full cycle. To introduce a spatially periodic refractive index modulation in nematic liquid crystalline waveguides a set of comb-shaped transparent ITO electrodes is placed on one of the glass surfaces. The applied bias allows tuning the structure from light confinement in one dimension, i.e. planar waveguiding, to bidimensional confinement. In the proposed geometry, the thickness of the liquid crystal layer changes linearly as a function of the transverse coordinate. In this way, both linear and nonlinear effective index changes are introduced in each waveguide.

Measurements of transport and non-linear optical properties in magnetic semiconductors Pb_1-xR_xX (R=Pr, Yb and X=S, Se, Te at x≈1-3%) were performed to elucidate an influence of magnetic ions on behavior of the charge carriers. It was shown that nonlinear optical methods may be used as a sensitive tool for investigation of electron-phonon an harmonicity near the low temperature semiconductor isolator phase transformation. The presence of the minimum in Pb_1-xPr_xTe at about T^ρ_min = 50 K in the temperature dependence of the resistivity r(T) is due to metal-semiconductor transition. Particularly with increasing of electron-phonon interactions indicated by temperature dependent Debye term (parameter β), one can observe an increase of two-photon oscillator strengths.

We investigated linear optical and second-order nonlinear optical (NLO) properties of films of urethane-urea copolymer (UU2) functionalised with a high concentration of an azobenzene chromophore. The polymer films on ITO-coated substrate were corona poled to induce a noncentrosymmetric organization of chromophore dipoles and data on the second harmonic generated with the laser beam (the fundamental wavelength 1053 nm, 6 ps/pulse, 20 Hz repetition rate) was acquired as a function of time and temperature. Second harmonic generation (SHG) was used to monitor in situ the polar alignment and relaxation of orientation of the side-chain Disperse Red-like chromophore molecules in the films poled at room temperature and high above the glass transition temperature (T_g 140-150^oC). The d_eff coefficient was determined from the Maker-fringe method and corrected for absorption. A strong second harmonic effect with a fast relaxation was observed in "cold" (room temperature) poling experiments. A large second-order resonantly enhanced optical nonlinearity (d₃₃ of the order of 200 pm/V) was obtained in high temperature poling. A strong and stable nonlinearity has persisted for years after the films were high-temperature poled.

Second harmonic generation was obtained with an interesting efficiency in thermally poled sulfide glass. The best results obtained to date for chalcogenide glasses were on a Ge-Sb-S system thanks to an adapted treatment of thermal poling. The poling parameters like temperature (100-310 °C), applied voltage (2.5-4 kV)and duration (5-60min) were explored. A large NL second-order susceptibility χ⁽²⁾ of about 10 ± 0.5 pm/V was measured. The nonlinear susceptibility profile as a function of the depth under the anode for Ge₂₅Sb₁₀S₆₅ poled glass was determined using the analyze of remained second harmonic signal during the NaOH etching treatment. In parallel, a study of the concentration variation of elements being able to be involved in the formation of a charge space was achieved by using the secondary ion mass spectroscopy.

We describe analytically and numerically dynamics of composite solitons consisting of nonlinearly coupled periodic lattice and localized components in self-focusing and self-defocusing nonlinear media, and identify the fundamental effects of gap merging and lattice phase modulation on the soliton motion. Our results can be applied to the problems of interaction of laser beams in nonlinear optical crystals and cross-phase-modulation of optical pulses in fibers.

Generation of high quality ultrashort optical pulses for optical communications in the 1,55 μm window is an important field of study. A key issue is the need to compress pulse width. Several techniques provide this compression functionality. Nonlinear Optical Loop Mirrors provide both compression and reshaping of the optical pulses. This work presents a comparative numerical study of several NOLM schemes whose results will be the basis for the design of a compact high quality ultrashort optical pulse source at 40 GBs with a monolithic InP semiconductor compressor. This source is under investigation within the MONOPLA project. A model based on the Nonlinear Schrödinger Equation is used. Input pulses are considered to be generated by a Gain Switching diode laser source. Characteristics such as time-bandwidth product, peak-power, pulse shape and pedestals are being considered.

Propagation of (3+1)D short light bullets in media with Kerr-like saturable nonlinearity is considered. The influence of higher-order terms - third order dispersion, nonlinear dispersion and self frequency shift are taken into account. A trial function corresponding to the product of (2+1)D gaussian beam and approximate solution of (1+1)D generalized nonlinear Schrodinger equation is applied. The Euler-Lagrange equations for varying temporal and spatial widths of the bullet are obtained. A stationary corresponding to small higher-order terms of these equations is found. The influence of material nonlinear coefficients for the stationary widths is discussed. The linearized form of Euler-Lagrange equations is obtained. The periods of oscillations of temporal and spatial width are found.

The performance of high-powered Wavelength Division Multiplexed (WDM) optical networks can be severely degraded due to the Four Wave Mixing (FWM) induced distortion. FWM distortion depends on the statistics of the signals carried by the WDM channels and hence the Gaussian approximation may not be valid. This implies that the well known Q-factor method can not be used to yield an accurate value for the performance of the system in terms of the Bit-Error Rate (BER) of the receiver. To evaluate the BER, one must determine the probability density function (PDF) of the decision variable in the presence of FWM noise, which is related to the signal statistics in a complex manner and can not be evaluated in closed form. In this paper, the Multi-Canonical Monte Carlo Method (MCMC) is used to calculate the PDF of the decision variable of a receiver, limited by FWM noise. Compared to the conventional Monte Carlo method previously used in the literature to estimate this PDF, the MCMC method is much faster and can accurately estimate very low Bit Error Rates. The method takes into account the correlation between the components of the FWM noise unlike the Gaussian model, which is shown not to provide accurate results. The impact of traffic burstiness in the performance of a FWM limited WDM receiver is also investigated using MCMC. It is shown that the traffic load can significantly affect the performance of the system.

This work presents theoretical and experimental studies of the energy efficiency of multiwave mixing in complex molecular media (dye solutions) exhibiting higher order nonlinearities. There is a great variety of such media, including the resonance ones revealing nonlinearities of higher orders due to the absorption saturation effect and transitions between different excited states of the molecules. However, the majority of previous studies of multiwave mixing have been performed in the resonant medium approximation disregarding the induced anisotropy effect. A new method for enhancement of multiwave mixing in solutions of laser dyes has been proposed and substantiated with the use of lasing as an additional light beam, whose absorption by the molecules in the excited states leads to the formation of thermal dynamic gratings resultant in the improved efficiency of the energy exchange. The theoretical models for the formation of nonlinear dynamic holograms adequately describing the control process over multiwave mixing by an independent light beam, the frequency of which is tuned into the induced absorption band from the molecules in the excited state, have been developed. Polarization multiwave mixing has been realized in Rhodamine-6G dye solution using nonlinearities up to the ninth order inclusive. It has been demonstrated that on orthogonal polarization of the hologram recording waves the diffraction efficiency is lowered by one-two orders, the diffracted wave polarization being dependent on the diffraction order (the polarization plane alignment is identical within the orders of the same evenness).

This work presents the results of theoretical and experimental studies into the processes of light field transformations upon multiwave mixing. The principal aim is to develop a theory of multiwave mixing in complex molecular media in conditions of exhibited internal (scattering from dynamic gratings) and external (resonator) feedback, to determine a mechanism of light field transformations at the dynamic holograms and by nonlinear interferometers, to work out and introduce into practice novel nonlinear-optical methods for the control over the energy and spatial-temporal characteristics of light beams. The possibilities for phase conjugation with simultaneous frequency conversion of a signal wave are analyzed. The methods aimed at the realization of various types of optical bistability, spatial hysteresis, regular and chaotic intensity oscillations are proposed and investigated.

In this work the different schemes of propagation and interaction of the light beams in nonlinear Fabry-Perot interferometer have been studied theoretically and experimentally. Degenerate and non-degenerate four-wave mixing have been realized in the cavity of Fabry-Perot type using Rhodamine-6G dye and polymethine dye 3274U solution as saturable absorber. The diffraction efficiency of intracavity dynamic grating has been studied in dependence on intensity of interacting beams and parameters of resonator. The theoretical model of the processes of intracavity degenerate and non-degenerate four-wave mixing has been developed and applied to the analysis of the efficiency of light beams conversion by mean of Bragg diffraction from intracavity dynamic gratings. For theoretical description of typical experimental situations we used the round-trip model of nonlinear interferometer adapted for the geometry of degenerate four-wave mixing, which can be realized in the scheme of symmetrical oblique incidence of pump, signal and probe beams to the front and back mirrors of cavity.

We propose the use of Dammann gratings commonly applied to problems in diffractive optics as a flexible tool for practical design of devices which perform multiple nonlinear optical frequency conversion processes, and which exhibit a bandpass grid-like quasiphase matched response in the wavevector mismatch space (Δk). By designing a periodic structure where several inversions in the sign of the nonlinear figure of merit take place at strategic locations within a fundamental period, baseband grid-like responses can be achieved in nonlinear materials consisting of sharp quasihase matching (QPM) peaks equally spaced in the wavevector mismatch space around Δk=0. With this design tool, the relative efficiency of the individual peaks in the grid can be arbitrarily set (equalization), including targeted suppression of specific nonlinear interactions in the grid (channel suppression). The baseband gratings so designed are then reallocated in Δk space by superimposing the baseband design on a suitable square carrier to achieve a targeted band-pass response. We present a simple procedure for the design of both baseband and bandpass Dammann gratings with examples of equalization and suppression in the context of nonlinear optics based on optimization algorithms. The tolerance of the designs under random variations of the inversion points and design quality parameters are also discussed.

The method of paraxial complex geometrical optics is presented to describe Gaussian beam diffraction in arbitrary smoothly inhomogeneous media, including lens-like media. The method modifies and specifies the results by Babic' (1968), Kirpichnikova (1971), Cerveny, Popov, Psencik (1982), Cerveny (1983, 2001), Timofeev (1995) and Pereverzev (1996) as applied to the optical problems. The method of paraxial complex geometrical optics reduces the problem of Gaussian beam diffraction in inhomogeneous media to the solution of the system of the ordinary differential equations of first order, which can be readily calculated numerically by the Runge-Kutta method. Thereby the paraxial complex geometrical optics radically simplifies description of Gaussian beam diffraction in inhomogeneous media as compared to the numerical methods of wave optics. By the way of example the known analytical solution for Gaussianbeam diffraction both in a free space and in lens-like medium (Bornatici, Maj 2003) are presented. It is pointed out, that the method of paraxial complex geometrical optics turns out to be equivalent to the solutions of the abridged parabolic wave equation.

The results of studying the steady states for bright and dark dissipative optical solitons, appearing in a single-mode semiconductor laser waveguide being periodically domained in a direction of passing the waves, are presented. These types of solitons occur due to reshaping the incoming optical pulses via the passive mode-locking process in traveling-wave regime. The relations between the pulse parameters and the waveguides' properties are chosen in such a way that the mode-locking process is incoherent in behavior that leads to the phase decay of the incoming pulses. The analysis demonstrates that bright and dark (with the shocked derivative in the shape of envelope) dissipative optical solitons can be supported by such waveguide with a quasi-linear gain and a fast-relaxing saturable absorption.

The process of doubling frequency of femtosecond pulse is considered in optical fiber with cubic and quadratic nonlinear response. Our computer simulation had shown a bistable (multistable) dependence of phase mismatching, conversion efficiency, duration of pulses from the total energy of interacting waves. Essentially, for constant total energy of interacting waves the solitons with various maximum intensity and their durations take place but their shapes remain unchanging. As a consequence, one can realize two stable states on phenomenon under consideration. The other application can conclude in encoding of information.

We investigated ultrafast nonlinear optical properties of periodic structures based on ZnSe/ZnS using interband and two-photon excitation of ZnSe sublatice by nano-, pico-, and femtosecond laser pulses. A considerable shift of reflection spectrum and large relative reflection changes were observed in a wide spectral range corresponding to the transparency region of ZnSe far from the intrinsic absorption onset. The nonlinear refraction is supposed to be controlled by population induced absorption changes in ZnSe and the relaxation time is controlled by a transition from non-equilibrium to quasi-equilibrium distribution of electrons and holes.

The results of numerical analysis of the influence of the initial pulse shape on the propagation of the pulses in a birefringent nonlinear single mode fiber are presented in the paper. The results are given in form of graphs of the input pulse threshold amplitude as a function of the fiber's birefringence. The threshold amplitude is the input pulse amplitude at which the fiber nonlinearity compensates the birefringence and makes the partial pulses travel with the same velocity. The following shapes of the initial pulse were investigated: hyperbolic secant, Gaussian, super Gaussian, super Gaussian second order. The analysis was carried out by numerically solving a pair of coupled Nonlinear Schrodinger Equations using the Split Step Fourier Method. It was assumed that both orthogonal polarization components of the fiber were excited equally. The calculations were performed for an optical fiber made of silica glass. The fiber attenuation was not taken into account.

We present an experimental and theoretical study of the nonlinear propagation of 90 fs laser pulses at 800 nm in bulk fused silica. An unexpected behavior of the off-axis emission for pulse energy corresponding to the supercontinuum generation threshold has been discovered. Our model, based on 3D Nonlinear Schrodinger Equation, well explains the observed nonlinear dynamics. For the first time we experimentally confirm that the onset of the supercontinuum generation is inevitably accompanied by the pulse collapse in transverse dimensions.

In our work we investigate the hexagonal matrix of cylindrical step-index waveguides placed inside a silica fiber. The linear and nonlinear parameters of the analyzed structure are optimized to observe discrete diffraction and creation of discrete spatial solitons. Numerical simulations were done for both focusing and defocusing Kerr-type nonlinearities.

A theoretical model has been developed for multiwave mixing in media with photorefractive nonlinearity, making it possible to describe the process of interaction between the waves in the conditions exhibiting nonlinearities of different orders with due regard for the mixing geometry. Theoretically, the process of N-wave mixing at the N - 1^th-order nonlinearity has been described with the help of a band model for the photorefractive nonlinearity mechanism that includes the transitions from impurity levels within the band gap and enables description of the diffusion or drift processes in the external electric field. The energy efficiency of multiwave mixing and geometric parameters of spatial solitons in photorefractive Bi₁₂TiO₂₀ crystals in the conditions of pulsed and continuous laser excitation have been studied experimentally. It has been found that switching-on of the photorefractive nonlinearity mechanism with 532 nmwavelength laser pulses requires a time interval in excess of 20 - 50 ns, with saturation beyond 80 ns. The formation dynamics of spatial solitons in photorefractive Bi₁₂TiO₂₀ crystals has been analyzed with the use of continuous-wave radiation of a He-Ne laser. It has been determined that the formation conditions and dynamics are influenced by a number of factors including the geometry of radiation input into a crystal, power of the light beam, orientation of its polarization in the directions of the crystal axes, applied electric field and its direction.

In this paper we propose a new method to control the spectroscopic and nonlinear-optical properties of photorefractive semiconductor CdTe crystals using the radiation defects caused by electrons and gamma-quanta irradiation. The photorefractive response is analyzed using the four-wave mixing pattern of laser pulses, one of which is delayed in time. It is found that both the irradiation and doping of cadmium telluride crystals with vanadium, titanium or ferrum leads to changes in the spectroscopic and nonlinear-optical properties of the crystals. Apart from relatively narrow bands appearing in the absorption spectra due to additional energy levels within the band gap, one can observe variations in the absorption factor over a wide spectral region. Recording of dynamic holograms is realized with no external electric field owing to pulsed laser radiation at a wavelength of 1.06 μm and diffraction efficiency of 1 - 2 %.

A study of optical vortices solitons propagation under the influence of an inhomogeneous external magnetic field is presented. The external magnetic field is applied on the z-axis, which is also the direction of propagation, so that a Faraday configuration is created. This study of magnetooptic vortices in a bulk, nonlinear, gyrotropic media leads to an investigation of the coupling of the electric field components, E_x and E_y, in the (x,y) plane. An optical beam propagating in the bulk is modelled by coupled equations in which the nonlinear refractive index is Kerr-like bulk optical nonlinearity. A transformation to rotating coordinates enables circularly polarised waves to be selected and a peak in the magnetisation over the centre of the beam is used. An important spatial dependence of the magnetisation parameter, defined as Q(x), stimulates novel singular behaviour. To demonstrate this kind of gyrotropy experimentally the usual Kerr nonlinearity may be too weak for comfortable observations but semi-magnetic semiconductors and atomic gases are shown to be possible candidates for which Faraday rotations are impressive.

We report the measurements of the linear and non linear absorption at 1064, 532 and 355 nm in samples of KDP crystals fabricated with the rapid growth process developed for NIF and LMJ high power lasers. Measurements were performed according to the ISO11551 standard by the "pulse" or "gradient" calorimetric method using a pulsed, diodepumped, Q-switched Nd:YAG laser. Time resolved spectroscopy method was used for the investigation of defects formation, responsible for the non linear absorption at 355 nm.

We report here thermal and non linear optics measurements: Photoinduced Second Harmonic Generation (PISHG) and Two Photon Absorption (TPA) measurements in the skutterudite RFe₄Sb₁₂ (R=Ce,La) and Ce_0.7Fe_3.5Ni_0.5Sb₁₂. The results show existence of important signal in LaFe₄Sb₁₂ compared to the CeFe₄Sb₁₂. At the same time the third-order Two-Photon Absorption (TPA) possesses maximums at low temperature. The introduction of Ni into the CeFe₄Sb₁₂ materials decreases clearly the PISHG and TPA signal.

In this work we propose a new form of two dimensional equations describing the light beam propagation in nonlinear planar waveguides. These equations utilize nonlinear planar waveguide modes, where both effective index and field envelope depend on light intensity. We compared results obtained by the new method with results obtained by application of the three dimensional beam propagation method and classical two-dimensional equations. It has been shown that the proposed method is much more accurate than the classical one. Additionally it can be easily extend to other than the Kerr type nonlinearities.

The photorefractive response of semi-insulating multiple quantum well structure operating with an external electric field applied along the quantum well planes to a localized illumination is investigated. An approximate steady-state relation between space-charge electric field and light intensity is found. To confirm used approximations, band transport model is numerically solved. The time evolution of the space-charge field is also analyzed.

The rule for both known magneto-optic effects in isotropic media is presented. It is a generalization of Faraday and Cotton-Mouton effects. This generalization includes any orientation of external magnetic field with regard to the light wave propagation direction. Also the formulae for total birefringence in medium placed within magnetic field has been given.