This PDF file contains the front matter associated with SPIE Proceedings Volume 6602, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

We put forward a scheme of the efficient terahertz and mid/far-infrared pulsed generation via an intracavity difference-frequency mixing of lasing fields due to the resonant intersubband and non-resonant bulk nonlinearities in the mode-locked dual-wavelength heterolasers.

We report experimental observations of the spectral modifications of ultrashort laser pulses caused by the generation of terahertz (THz) radiation via phase-matched optical rectification in LiNbO₃. The measured red shift and narrowing of the laser pulse spectra is in a good agreement with the consideration of the THz generation processes in terms of difference frequency mixing. Moreover, we propose and demonstrate a new method for evaluating the absolute energy of the THz pulse generated via high-efficiency optical rectification. The method is based on analyzing the laser pulse spectral modifications. Abilities to obtain >100% optical-to-THz quantum conversion efficiency are discussed.

Space-time dynamics of singularities and optical diabolos birth, transformations and annihilation in developing generic light fields was measured first by elaborated technique of high time-resolution digital Stokes polarimetry. Duration of singularities and diabolos "life" is defined by many-step topological reactions between hyperbolic and elliptic diabolos.

A novel type of quasi-nondiffracting (elongated) speckle fields having the vortex structure of individual speckles is investigated. A physical mechanism of forming the elongated vortex fields is established. Two optical schemes for forming such fields are proposed and realized.

We study the angular structure of polarization of light transmitted through a nematic liquid crystal (NLC) cell by analyzing the polarization state as a function of the incidence angles. Our theoretical results are obtained by evaluating the Stokes parameters that characterize the polarization state of plane waves propagating through the NLC layer at varying direction of incidence. Using the Stokes polarimetry technique we carried out the measurements of the polarization resolved conoscopic patterns emerging after the homeotropically aligned NLC cell illuminated by the convergent light beam. The resulting polarization resolved angular patterns are described both theoretically and experimentally in terms of the polarization singularities such as C-points (points of circular polarization) and L-lines (lines of linear polarization). When the ellipticity of the incident light varies, the angular patterns are found to undergo transformations involving the processes of creation and annihilation of the C-points.

The space-time dynamics of a pulsed Bessel beam envelope behind the axicon is studied in detail theoretically and experimentally. It has been discovered and explained the phenomenon of appearance of an additional pulsed beam (satellite) behind the axicon. The dependence of the axial intensity of the output diverging femtosecond Bessel beams on the distance from the axicon has been calculated and measured. It is established that the Bessel pulsed beam diameter increases, the axial intensity slowly decreases with increasing the longitudinal coordinate, and the zone of existing the pulsed Bessel beam is very long. It is shown that in schemes with the diverging and converging initial Gaussian pulse differing in the lens position, one can generate femtosecond Bessel beam with the required parameters (zero-maximum diameter and intensity) using only a single axicon and a lens.

A general study of transverse energy flows (TEF) as physically meaningful and informative characteristics of paraxial light beams' spatial structure is presented. The total TEF can be decomposed into the spin and orbital contributions giving rise to the spin and orbital angular momentums, correspondingly. Definitions and properties of these constituents are discussed in relation with the optical field representation through linear and circular orthogonal polarization bases. An analysis of TEFs near singular points has been carried out. General discussion of the evolution of the optical field singularities is presented. Possible mechanical action of light beams associated with the TEF is studied on the example of an absorptive medium described by the Drude-Lorentz model.

A new method of formation and spatial separation of radially and azimuthally polarized Bessel beams containing phase dislocation (Bessel vortex) is proposed. This method is based on using one-dimensional photonic crystal. It has been shown that on the bases of these structures effective and compact generators for radially and azimuthally polarized Bessel beams can be elaborated.

Spontaneously grown partially ordered domain structures in SBO crystals are characterized via nonlinear diffraction. Domains have the form of sheets lying in cb plane with the domain walls oriented perpendicularly to the a crystallographic axis. The thickness of domains varies in quite wide range. The effective thickness of domains contributing to the nonlinear diffraction is determined from Fourier spectrum of inverse superlattice wave vectors to lie between 180 nm and 8 microns. General properties of spatial Fourier spectrum are reproducible from one growth procedure to another, however, details of spectrum noticeably vary. Enhancement factors for random QPM are calculated and found to be of order of several thousand in the near UV.

Currently coherent spin phenomena are in the focus of wide research activity in such multidisciplinary fields as spintronics, quantum communication and information processing.^1-3 Among those, the optical orientation based on the transfer to media of the angular momentum carried by the circularly-polarized light plays very important role for disclosing basic processes that govern generation and relaxation of spin and orbital states. By using ultrafast pump-probe spectroscopy we show that optical pumping can induce spin-polarization in antiferromagnetic Mott insulators R₂CuO₄ (R = Pr, Nd, Sm) providing a way for fast nonlinear manipulation of spin states on time scale of 100 fs and less. The driving mechanisms of the ultrafast spin orientation and dynamics in Mott insulators are the strong spin-orbit, spin-phonon and exchange interaction as inherent features of strongly-correlated systems both in the ground and excited states. High values of the corresponding nonlinear susceptibilities may have significant impact for novel ultrafast all-optical technologies.

By third-order nonlinear coupling and tightly focusing the beams in a single crystal of BBO, high intensity broad-bandwidth femtosecond pulses are used to generate 50&mgr;J of light at 270nm (up to 1% THG efficiency). And it is proved that the major contribution to the THG observed is the third-order process, not the cascaded second-order process.

We demonstrate both experimentally and theoretically that efficient frequency down-shifting of an optical soliton pulse can be realized in a dispersion decreasing fiber. This effect relies on the Raman self-frequency shifting that can occur with high efficiency due to the adiabatic compression of the pulse and therefore reaching higher intensities in a fiber with monotonically decreasing anomalous dispersion. A smooth frequency shifting of 90 fs soliton pulses in the 1.55-1.8 &mgr;m range is demonstrated.

Among the frequency conversion methods for three-dimensional images characterized by a complex wave front, of particular interest are those based on nonlinear dynamic hologram recording. The use of resonant media including the solutions of complex organic compounds looks promising for realization of the process over wide temporal and spectral ranges. The formation of dynamic holograms in such media is caused by changes in the refractive index and absorption coefficient when the molecules are activated to higher energy states and also by thermal nonlinearity due to the medium heating. In this work, the schemes for visualization of infrared images on multiwave mixing in dye solutions are analyzed both theoretically and experimentally. To improve the frequency conversion efficiency, an intracavity recording method for nonlinear dynamic holograms is used. The pattern of a light beam with the wave front dislocations is demonstrated.

We study theoretically an opportunity of shaping three-wave coupled states within a strong co-directional collinear acousto-optical interaction between two optical waves and the suffering losses acoustic pulses in a square-law nonlinear crystal. The developed analytical model for this process with the mismatched wave numbers describes a regime of coupled modes, which is considered analytically, using the first order approximations as well as qualitative estimations, and simulated numerically. The comparison of results from these two approaches demonstrates their acceptable agreement with each other. Three-wave collinear acousto-optical coupled states originating within such an interaction exhibit a remarkable asymmetry in shapes of their envelopes and a shift of extrema in the intensity distribution for each wave component.

Non-linear polarization rotation of femtosecond laser radiation with intensity of the order of 10¹³ W/cm² in BaF₂ crystal under plasma formation conditions was investigated. Abnormal behavior of cross-polarized wave generation efficiency on laser pulse energy may be explained by influence on the process of polarization anisotropy of fifth order non-linearity.

Infrared supercontinuum from a large mode-area photonic-crystal fiber (PCF) for varied fiber lengths, powers and in dependence on the fiber mode structure under the 15 picosecond pulse excitation at the 1.08 μm pump wavelength with the coupled powers up to the PCF damage threshold are studied both experimentally and numerically. The conversion efficiency into a spectrum ranging up to 1.9 μm reaches 33%. The four-wave mixing is found to be dominating mechanism forming the supercontinuum structure. It is shown, that the supercontinuum bandwidth cannot be increased by only growth of the propagation length because there exists the optimum one. The analysis of inter-mode cross-modulation effecting supercontinuum smoothness, bandwidth and its temporal characteristics is presented.

Formation of light fields with preset intensity is of the interest for different laser applications. Spiral beams optics is the universal method of such fields generation. One of the experimental ways of spiral beams formation is the astigmatic transform of specially realized one-dimensional light field to the intended spiral beam. The presence of phase singularities is the feature of spiral beams. Traditional interference detection of singularities of spiral beams can be inconvenient if the number of isolated zeros located within the low intensity area. It is typically for beams in the shape of closed curves. The same astigmatic transform can also be used for the beams analysis.

Coherent phase control under the interaction between bichromatic radiation with multiple frequencies and quantum systems is the topic of the last time investigations both experimental and theoretical. This type of nonlinear optical control enables one to manipulate the characteristics of radiation processes by the change of the relative phase of bichromatic field. The present study is devoted to the theoretical analysis of the coherent control of two-level system behavior under bichromatic excitation in the frame of perturbation approach. The general expressions have been derived which are valid for any integer ratio n between the frequencies of monochromatic components of radiation. Obtained formulas describe the system characteristics as functions of relative phase of bichromatic field and other radiation parameters. Bichromatic excitation of Rubidium atom is considered as numerical example.

Experimental data and theoretical model describing stochastic pulsations within oscillatory mode of superradiant emission from the LaF₃ medium doped with impurity praseodymium ions are presented. The model deals with three-level system with close upper levels and reflects our experimental data on fluorescence of praseodymium ions. The mean-field approximation is used to develop the superradiance theory. In determined case basic equations of the developed model are reduced to well known Lorenz equations of deterministic chaotic dynamics.

The period of nutation oscillations near the leading edge of a rectangular electromagnetic pulse interacting with ensemble of quantum dots is shown to be defined by the main parameters describing the electromagnetically induced electron transfer.

We have demonstrated a good quality of visualization of phase objects by nonlinear phase contrast technique with photothermal Zernike cell. The technique requires submilliwatt power of the illuminated laser beam. The image-intensity- inversion process was also observed.

The polarization and spatio-temporal dynamics of coherent pulses propagating in an active birefringent Kerr non-linear fiber are discussed basing on the numerical solutions of the fiber effects full set self-consistent system of equations for the circularly polarized components of a coherent optical pulse coupled to the ensemble of the doped resonance atoms.

In this work thermal and temporal changes of the light scattering by lithium niobate crystals have been investigated under steady illumination by argon ion laser beam (λ = 514.5 nm) in the temperature range of 20-800°C and have been observed the anomalies on the temperature curves of elastic light scattering intensity near of 100, 200 and 350°C for the nominally pure crystals and near 100 and 200°C for iron doped one if laser beam was directed along the c-axis of crystal. Oscillations of light scattering intensity have been discovered on the screen in far field at room temperature. The period of oscillations dependence on the kind of impurities, concentration and power of illumination. Laser beam in this case was directed perpendicular to c-axis of crystal. Pulsations were spreading along the c-axis. The threshold of power is about of 100 mW.

We consider optical 1D envelope solitons in Kerr dielectric with cubic nonlinearity and use two-solitons configurations for modelling entangled states of photons. We calculate spin, momentum and energy of solitons on the basis of approximate solutions to the nonlinear Maxwell equations and construct entangled two-solitons singlet states in special stochastic representation.

Specific features of two-photon nutation in a system of coherent biexcitons in CuCl-type semiconductors are studied. It is shown that, depending on the parameters of the system, nutation represents a process of periodic conversion of photon pairs into biexcitons and vice versa. The possibility of phase control of optical nutation is predicted.

Taking into account the exciton-photon and elastic exciton-exciton interactions we investigated peculiarities of transmission of supershort light pulses by thin semiconductor films. We predict the appearance of time dependent phase modulation and dynamical red and blue shifts of transmitted pulse.

We conduct a theoretical analysis of the Stokes component mode structure of the Raman scattering. The Raman scattering is excited in a multimode waveguide with pump radiation having statistics corresponding to the model of the narrow-band Gaussian noise. We obtain an analytical relation connecting the number of spatially coherent modes of the Stokes component, characteristics of the waveguide and conditions of the Raman scattering excitation. It follows from the obtained relation that the Raman scattering spatial coherency degree at the waveguide's exit is determined by the number of the spatial modes of pump radiation and the amplification of the Stokes radiation throughout the waveguide's length. There exists a threshold in the amplification corresponding to the unlimited increase of the number of the spatially coherent modes of the Raman scattering and therefore to a zero of spatial coherency. Conducted estimations show that at the Raman scattering threshold value of the radiation intensity the number of the spatially coherent modes of the Raman scattering Stokes component should be comparable to that of the thermal source. Experimentally, measured dispersion of the spatial intensity fluctuations of the Stokes component isolated with an interference filter (spectral bandwidth ~ 1nm, λ = 620nm) is three time smaller than that of the luminescent lamp radiation

We conduct a theoretical analysis of two models of transformation the spatial coherency transformation of the radiation propagating in the multi-mode waveguide. For each of them we obtain analytical relations connecting the number of spatially-coherent modes of the radiation appearing in the waveguide, parameters of the incoming radiation and the characteristics of the waveguide. We assess the efficiency of the radiation de correlation at various initial spatial statistics of the radiation and its quasi-nonstationary non-linear interaction with the waveguide's core. We find that the main factor limiting the de-correlation level of the light beams in the multi-mode waveguide with quartz core is the excitation of the Raman scattering. Raman scattering decreases the effective intensity of the radiation at the original frequency and the changes the dynamics of the phase-amplitude transformation of light.

The spectral and polarization properties of fluorescence in dye solutions on two-photon excitation are studied. The conditions influencing a relative contribution of various mechanisms underlying the formation of a virtual intermediate state in the process of two-photon fluorescence excitation are determined. It is demonstrated that they are associated with the polarization and frequency characteristics of excitation fluxes and also with the electronic-vibrational molecular structure

The Zeeman splitting of NO molecule ro-vibrational spectral lines in strong magnetic field was calculated and compared with experimental data. The nonlinear Zeeman splitting takes place in magnetic field of ~1 T and stronger.

The influence of magnetic field on terahertz pulse generation from InAs surface excited by femtosecond laser radiation is considered. We propose an analytical model describing the non monotonic dependence of THz emission on magnetic field. It has been found that under magnetic field of about 2-3 T the efficiency of terahertz emission enhances in 5-6 times. Monte Carlo simulation performed gives nearly the same results.

Basic characteristics of visualization process of transparent objects are analyzed and calculated when phase-contrast technique with photothermal Zernike cell is employed. Edge enhancement effect is observed under the conditions, when sizes of illuminating beam and investigated object are comparable. It is demonstrated that the visualization process has a resolution close to the diffraction one. Numerical results of the visualization process in a scheme with photothermal cell are compared to the results obtained in the same schemes with Zernike cell based on local Kerr nonlinearity and with traditional linear Zernike plate.

Optical code division multiple access (OCDMA) is a promising multiple-access technique for future all optical networks. In this manuscript, the usefulness of exploiting bistable optical elements as threshold devices in coherent OCDMA systems is analytically investigated, in which the bistability effect is modeled by a simple square loop.

The effect of electromagnetically induced transparency on the spectrum of defect modes of one-dimensional photonic crystal is discussed theoretically. Narrowing of defect mode linewidth is predicted due to nonabsorbing highly dispersive medium in defect layer.

Broadband THz pulse generation via optical rectification of femtosecond laser pulse is studied. We optimize the phase-matching conditions by taking into account the material dispersion properties of ZnTe and GaP crystals, with are measured and modeled. Laser pulse duration influence is studied.

A solid-state dye laser with a microcavity whose size is comparable to the lasing wavelength is modeled by means of the finite element method. The position of the pumping source affects the lasing mode spectrum. In comparison with a single point source at the edge of the cavity, a random distribution of excitation sources in the central gain part of the microcavity leads to depletion of odd longitudinal modes and to higher output efficiency of the laser radiation in even modes. The simulation results are explained by simple physical considerations.

Wavelength tunability of a microcavity solid-state dye laser is modeled by means of the finite element method. We investigate the application of two phenomena, thermoelastic expansion of the microcavity material and thermo-induced change of refractive index, in order to tune microcavity mode frequencies by the variation of the effective optical path. An optimized size of the laser microcavity is defined depending on the operation wavelength bandwidth and the glass temperature of the gain material.

Based on the theoretical symmetry analysis of the nonlinear electric susceptibility, second harmonic generation is examined as a probe for detection of various type of ordering: magnetic, ferroelectric, ferroelastic. The nonlinear optical response of multiferroics is illustrated by the example of bismuth ferrite BiFeO₃. It is shown that magnetically induced second harmonic response as well as anisotropic part of ferroelectrically induced second harmonic depends on mechanical (ferroelastic) ordering. This is one of the aspects of order parameters coupling in multiferroics.

Differential transfer matrix method is extended to analyze nonuniform nonlinear distributed feedback structures. The input-intensity dependence of the reflectivity and transmissivity of inhomogeneous nonlinear dielectric slabs is investigated for TE polarized and TM polarized incident waves.

The hyper-Raman scattering by LO phonons is theoretically investigated, taking into account the Wannier excitons as intermediate virtual states. The different scattering mechanisms are considered. The hyper-Raman efficiency as a function of the energy of incident photons is calculated for ZnSe, ZnO, CdS and GaN.

Unlike mean-field approach that was used in previous statistical model, in this paper we use a new approximation to excitation back transfer accounting for variance in population of the first excited level. Based on the results, we find that for concentrations of erbium ions more than critical, upconversion rate calculations deviate substantially from the calculations based on simplified model.

The Bragg solitary waves in the form of five-wave weakly coupled states, occurring within a four-order non-collinear scattering of light by acoustic wave in an optically anisotropic tellurium dioxide (TeO₂) crystal, are considered. An exact analytical description, based on the amplitude evolution equations including the phase mismatches, is adduced. The photo-elastic effect with contributions of the optical activity is estimated in a tellurium dioxide crystal. Originating five-wave weakly coupled acousto-optical states is developed through formulation of the localization conditions for multi-pulse states in the case of an exact phase synchronism. Spatial distributions for the optical components of multi-pulse coupled states are simulated and discussed.

We consider implementation of coupled nonlinear optical processes in aperiodically poled nonlinear crystals which can be produced by the method of the nonlinearity modulation superposition. The wave interaction consisting of three three-frequency processes with multiple frequencies, is analyzed in detail. It is shown that under certain conditions the superposition of waves, generated in this case, can form the light pulses with subfemtosecond duration.

Paper contains experimental results and theoretical estimations of quasi-phase matched second harmonic generation in PPLN, where the nonlinear grating vector is noncollinear to wave vectors of fundamental radiation and its second harmonic.

The report is devoted to an analytical solution and computer simulation of the THG for femtosecond pulses taking into account self- and cross- modulation of interacting waves. As it is well known, for the case under consideration because of pulses self-action the low efficiency of frequency conversion takes place for phase and group wave matching as rule. Therefore, in physical experiment, the THG is realized on the base of SHG and then summary frequency wave generation for waves with basic and doubling frequencies. Using an original approach, we obtained an explicit solution of Schrödinger equations describing THG in the framework of longer duration of pulses. It should be stressed, that the main feature of our approach is an using of conservation laws for interacting waves. We found various regime of trebling frequency and shown that under some conditions the THG process has a bistable features on conversion efficiency. On the base of our solution we show an existence of two regimes: one of them corresponds to low frequency conversion efficiency and other to high one. It is very important for practice realization that switching between two stable states can be realized due to changing of phase mismatching in short intervals of its values. It should be noticed that computer simulation results, which are obtained with taking into account second order dispersion and without it, has confirmed analytical results. For computer simulation, we constructed conservative difference scheme, which gave a possibility to made simulation with high accuracy.

The paper is devoted to an analytical solution of SFW generation for femtosecond pulses taking into account the quadratic and cubic nonlinear response of medium. Using analytical solution, which obtained in the framework of long pulses approximation, the generation regimes are analyzed. It was shown that there are generation regimes with high and low efficiency and they exist simultaneously for given set of laser pulses interaction parameters. It means that there is a bistable process of generation. Optimal input intensities of two waves for achievement of region of generation of summary frequency wave with high efficiency were found. This property of frequency conversion can be used for creation of all optical switching. The switching between two stable states can be realized due to introducing of phase mismatching in definite section of nonlinear medium. It should be noticed that computer simulation results that are made with taking into account second order dispersion and without it confirm the analytical results.

The properties of transformation of a supershort light pulse with arbitrary temporal form in dispersive media in the third approximation of the dispersion theory are investigated. The special attention is devoted to the cases having practical importance, for example, when temporal form of the pulse is described by the function of hyperbolic secant. It is shown that in the spectral region of 'zero' dispersion owing to the influence of dispersive effects of the third order the deformation of envelope of the pulse takes place, namely: the maximum of the envelope is decreased, shifted and the satellite appears.

Fabry-Perot interferometer with two identical waveguide gratings mirrors is studied. Earlier we studied the case of oblique light incidence and in this paper normal incidence is considered. Normal incidence case is special because two waveguide modes propagating in the opposite directions are excited simultaneously. It is found that for the filter having small distance between the waveguide grating mirrors the reflection spectrum depends on the phase shift between the gratings. One or two additional resonances appear in the case of phase shift not being equal to 0 or π. We attribute the appearance of these resonances to the symmetry breakdown in the waveguide system and coupling between the waveguides.

The orientational self-action of a light beam in (1) transparent planar nematic liquid crystal (NLC) subjected to external DC field and (2) planar NLC doped with stilbene dye in the absence of external field has been studied. It is shown that the shapes of the aberrational patterns developed in the far-field diffraction zone are highly asymmetric, unlike the common system of concentric rings. In case (1) the aberrational pattern exhibits complex dynamics of its formation. The shape of the pattern is independent of the polarization of the incident light. In case (2), the divergence of the pattern does depend on the incident-light polarization. In both cases, the light-induced director deformation in the field of the ordinary wave was found. The physical mechanisms of the director reorientation responsible for the asymmetric aberrational patterns are discussed.

Properties of achromatic volume image, recorded on photoresist, are viewed in the given article. The image is characterized by saw-tooth holographic grating profile. The mentioned property is utilized for production of holographic protective elements being impossible to copy by holographic means, deter for counterfeiting and difficult to imitate.