Search

Carbon exhibits a remarkable range of structural forms, due to the availability of sp

Correlation properties of light beams upon self-phase modulation in a thin layer of a medium with thermal nonlinearity are studied. It is found out that the efficiency of spatial coherence transformation of radiation is determined by the ratio of the characteristic coherence radius of the initial radiation to the size of phase inhomogeneities induced in the nonlinear medium.

The destruction of the spatial coherence of multimode laser radiation in a delay-line-based system is analysed theoretically and experimentally. A scheme of a coherence-transforming device operating in a broad wavelength range and various lasing regimes is proposed. This scheme is shown to be efficient for rapid speckle-noise suppression in optical recording and lithography.

The introduction of artificial pinning sites in YBa(2)Cu(3)O(7-delta) (YBCO) epitaxial thin films has been obtained by pulsed laser deposition (PLD) technique from YBCO-BaZrO(3) (BZO) composite targets with BZO concentration ranging from 2.5 to 7 mol %. The typical critical temperature, T(c), drop observed in YBCO-secondary phase films grown by PLD has been successfully recovered by increasing the deposition temperature. Transport properties analyses revealed improved pinning force values for YBCO-BZO films for BZO concentration above 5 mol %. These films exhibited an anomalous dual peak structure which has been ascribed to the presence of two pinning contributions. The crossover field, B(m), separating these two pinning regimes has been observed to be temperature independent suggesting the occurrence of the matching field effect. The measured value of B(m) agreed with the matching field value, B(Phi)=Kn(d)Phi(0), as evaluated from transmission electron microscopy investigations. The mark of this phenomenon is retained down to 10 K, making YBCO-BZO more performing than pristine YBCO films at applied magnetic fields below B(m) in all the temperature range inspected. On the contrary, in the high magnetic field range (above B(m)), the effectiveness of correlated pinning is progressively reduced on lowering the temperature suggesting that at low temperatures the dominant pinning contribution arises from isotropic pinning centers. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3477451]

The steady interest in nonlinear systems of optical data processing that has been shown in the last few decades is due to the prospects of direct optical image transformation and control of the space-time structure of light fields. The first investigations in this field dating back to the 1960s were developed by generalizing the ideas and methods of traditional (static) holography as applied to the processes of recording and processing the wave fields in nonlinear media. Subsequently, a close relationship between dynamic holography and nonlinear optics was established. The works along these lines revealed the phenomenon of wave-front reversal (phase conjugation) of light beams under four-wave mixing (FWM) [1]. The upsurge of investigations on the phase-conjugation optics in the 1980s set new ways in using dynamic gratings for solving various problems of transformation of the space-time structure of light fields (phase-distortion compensation, radiation self-focusing on a target, associative holographic memory, dynamic grating lasers, etc.) [2]. At the same time, the discovery in the mid-1970s of the phenomenon of optical bistability revealed at lightbeam propagation in a nonlinear Fabry–Perot interferometer filled with sodium vapors is noteworthy [3]. The investigations along these lines made it possible to devise a transphasor (an optical analog for the transistor) and optical limiters and to develop an optical memory system. The nonlinear interferometers proved to be very convenient systems for modeling various effects of self-organization. On their basis various dynamic regimes, including regenerative intensity pulsations and the transition to optical chaos were investigated [4]. In the last decade, nonlinear systems for controlling the spatial structure of laser beams received a large development effort [5]. Methods for generating light fields of new types — stationary spatially modulated, rotating, helical, and turbulent — ones were proposed. Analysis of the interaction of two light waves of equal input intensity at their counterpropagation in a nonlinear ring cavity revealed a new regime of optical bistability in which energy transfer from the less intense light beam to the more powerful one takes place and the effect of interferometer transmission asymmetry for two light beams with a practically equal input intensity is observed [6]. This effect, named asymmetric optical bistability, was also predicted later for the case of symmetric incidence of two light beams on the input mirror of a Kerr-nonlinearity Fabry– Perot interferometer [7]. The dynamics of nonlinear-optical systems under the conditions of symmetry breaking bifurcation was investigated by an example of anisotropic lasers with a saturating absorber [8] as well as in a distributed feedback system (Bragg grating) at counterpropagation of two light beams [9].

A model for the calculation of heating of a blood vessel, which is modeled by an infinite circular cylinder and located in the hypodermic layer, under the action of laser radiation is proposed. Heating of such a vessel under the action of radiation with wavelengths most often used for laser therapy is calculated within the framework of the model proposed. The heating process is compared with the case of skin heating by laser radiation in the multilayer model of the skin.

The transient thermal grating (TTG) technique in transmitting geometry has been applied to the characterisation of thin-film thermal diffusivity. The thermal grating is initially formed in a film surrounded by two substrates The theoretical background and experimental data for diffraction active and nonactive substrates are described. A one-dimensional model of heat diffusion in a three-layer structure fits the experimental data of TTG decay well if the film thickness is less than the thermal grating period. In addition, film thickness, light absorption coefficient in a film, and thermal properties of substrates influence the TTG relaxation time. The optimum experimental conditions have been selected, and the method of thermal diffusivity characterisation of thin films has been devised.

The contrast inversion of a DFWM-conjugate wave which is realised by a π-shift of its zeroth harmonic with respect to the remainders has been first investigated. The experimental results for a one-dimensional object and computer-calculated data for space-distributed amplitude obstacles are discussed.

A scheme for the formation and reconstruction, at the doubled frequency, of volume dynamic holograms is considered in the case of the fifth-order nonlinearity. The results are given of an experimental investigation of the diffraction of laser radiation by a transmission dynamic grating formed in a solution of polymethine dye No.3274U. A theoretical model is proposed for describing quadratic hologram formation and suitable for calculation of the energy efficiency of conversion of the radiation frequency.

Method of increasing the efficiency and quality of associative (by a fragment) data retrieval in the resulting zero reflective order of a system, composed of a thin off-axis hologram and a feedback mirror, situated in its -1-st diffractin order, is considered on the example of lensless Fourier-holograms. As a feedback mirror an adopted static phase-conjugating mirror is used based on hologram of mutally conjoined waves.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

It is theoretically shown on the example of a lensless Fourier hologram, that additional channels of associative data reconstruction are possible in the system, composed of a thin linear superimposed off-axis hologram and a phase-conjugating mirror. Due to the "phase-retaining" nature of a phase-conjugating mirror, partial transformation of noise field components (which are nonlinear on amplitudes of fields and can't be interpreted as an image or a correlation peak) into information field components takes place in such a system. Taking it into account and assuming certain opportunities of phase-conjugating reflection control make it possible to consider the system as a quadratic hologram with modifiable response. Possibilities of data processing by all the channels are considered.

This article is aimed at elucidation of the specific features in propagation of ultrasound waves in an electrostructurized medium, of their dependence on an applied electric field and implementation of the effects obtained in practice.

The present work is aimed at elucidation of the specific features in propagation of ultrasound waves in an electrostructurized medium, of their dependence on an applied electric field and implementation of the effects obtained in practice. In experiments, the use was made of electrosensitive liquid interlayers, which manifest the essential dependence of viscoelastic-plastic properties on a magnitude of an electric field applied to shear macroflows. The basis of a homogeneous suspension was the transformer oil, to which the finely divided silica powder, the corresponding surfactant and activator were added. To determine the velocity of ultrasound propagation in liquid media, the time of ultrasound signal propagation was compared with the delay time of the reference signal in the standard delay line.

Long-lived transient gratings excited by UV laser radiation in the absorption band of synthetic diamond crystals have been observed for the first time. Decay constants of the gratings depend on the crystal defects nature and lie in the range of 0.1-100 ms that is 103-104 larger than that of thermal gratings. They are observed as slow tails of the scans which describe the time evolution of the signal diffracted by the laser induced grating in the crystal. Electron-paramagnetic- resonance shows a correlation between the EPR signal and long-lived grating amplitude. The defects with unpaired electrons are mainly responsible for the gratings observed. Selectivity of the long-lived gratings to the wavelength of excitation is shown. The gratings reveal a strong sensitivity to the crystal temperature. For example, the grating lifetime decreases by several orders of magnitude when the crystal temperature increases from 20 degree(s)C to 200 degree(s)C. It proves the defect nature of the gratings observed. Light-induced grating approach appears to be a sensitive tool for the investigation of defects in diamond crystals including those that do not yield the luminescence.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this work we give a retrospective analysis of the development of optical technologies in Belarus. In the post-war period a great scientific and technological potential has been built up in this sphere, highly skilled specialist have been trained and prestigious scientific and technical schools have appeared. Belarusian multiprofile optical industry is noticed to be capable of producing not only the materials and equipment for optical production but also optical goods of the highest level of complication. The characteristics of cosmic photoequipment, photogrammetric and cinetheodolite techniques, a variety of laser devices and optical goods for civic purposes are given as an example. The instances demonstrating the realization of unique optical projects are considered as well. High quality of Belarusian optical production makes it be much in demand in Russia, Japan, USA, Germany, France, China, Korea, Sweden, Spain, England, United Arab Emirates and other countries.

The approach is suggested, which permits more full description of correlation responses of thin holograms with superposed registration on the basis of account of contributions from all the nonlinear with respect to the recorded object fields inter- and cross-modulation diffraction structures. Based on this approach, from the common point of view the associative reconstruction of information by the thin quadratic off-axis hologram and the linear off-axis hologram -- phase-conjugate mirror system was considered.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Phenomenological analysis is made of analogue associative processors based on thin holograms with superimposed registration. Possibilities of realization of functions of associative memory, associative highlighting of common fragments of object scenes, novelty filter and static phase- conjugate mirror are investigated on the basis of utilization of informative properties of a quadratic off- axis hologram, a hologram of mutually conjugated waves and a system, composed of a linear off-axis hologram and a phase- conjugate mirror.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Associative properties of a thin quadratic off-axis hologram and a hologram of mutually conjugated waves are theoretically investigated, on the basis of phenomenological analysis of informative structure of correlation responses. Mechanisms of reconstruction of information in a system, composed of a thin linear off-axis hologram and a phase- conjugate mirror are investigated, including the mechanism of transformation of 'noise components of field into informative ones.

A theoretical investigation into the dynamics of Fabry-Perot interferometer (FPI) with multilevel resonant medium has been conducted. The origin conditions and characteristics of complex dynamic operating modes of FPI have been analyzed at constant intensity of the input light beam. The mechanisms of switching from regular intensity oscillations to the chaotic ones through the sequence of period-doubling bifurcations or multiple pass Shilnikov's attractor have been demonstrated.

The layered systems consisting of one and two boundaries have been studied by the method of thermal dynamic gratings. One-dimension theory has been developed for description of a well conducting interface in three-layer structure. Acoustic oscillations caused by the spatially periodic heating of air or ethanol that are in thermal contact with absorbing solid surface have been observed.

Time evolution of the intensity of light diffracted by phase grating which is induced by thermal dynamic grating (TDG) in liquid film between glass or quartz substrates is studied theoretically and experimentally. Due to heat exchange at the film boundaries the thermal gratings are also formed in substrates. The diffraction intensity of substrates can be less or comparable to that of film (non-active and active substrates, respectively). The experimental results are in a good agreement with the theoretical calculations carried out for the case when the film thickness is less the TDG period. It is shown the essential influence of the film thickness and the active-substrates contribution on the evolution of the intensity of diffracted light.

The radial distribution of Gaussian beams radiation intensity on the focal plain of the ocular optical system has been calculated using the human eye Modulation Transfer Function. The dependencies of the distribution on the distance to the beam's constriction have been analyzed for the visible spectral range at a given eye accommodation. More consideration has been given to the conditions of the most `sharp' focusing of laser beams onto the retina (the most dangerous cases) and to the typical errors arising in the process retinal irradiance distribution measurement through the pupil. The analogous model has been created for the eyes of some animals. The results of calculations are in a good agreement with direct measurements data at the back pole of enucleated rabbit eyes.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The important role is theoretically shown of processes of transformation of noise components of field, nonlinear in registered object field, into informational ones at reconstruction of information in system, composed of thin linear off-axis hologram (with one or several registered images) and wide-aperture phase-conjugate mirror, working in linear regime. It is shown, that for associative reconstruction of information the second, being formed at the repeat scattering by hologram, order of diffraction of the system may be used, at scattering into which noises reconstruct whole object fields.

The article deals with the determination of deformations of the human jaw bone under functional loads using holographic interferometry. Quantitative evaluation of interferograms of the mandible has been carried out. The deformations in horizontal and frontal planes on the level of the alveolar process, body, and lower edge of the jaw were determined.

The possibility of generation in a nonlinear interferometer of the complex-form intensity pulsations through the concurrent resonance nonlinearities due to transitions of molecules to different energy states has been put forward and substantiated. The conditions and character of transition to the mode of dynamic chaos have been analyzed.

The possibility of phase conjugation with simultaneous doubling of the light-wave phase and frequency upon nondegenerate four-wave mixing has been suggested and substantiated theoretically. The dependence of the energy efficiency of double-phase conjugation on the spectroscopic characteristics of the multilevel resonant media has been analyzed.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The characteristic features of the conjugate wave's formation under transient four-wave mixing in a two-level medium are investigated. The phase modulations of the signal and conjugate waves induced in the four-wave mixing are not mutually conjugate and have the same sign. The fulfillment of the phase-conjugation for the phase modulated signal has been shown in particular to be connected with the envelope's deformation and the spectrum's change of signal pulses. The transient optical bistability connected with the nonlinear absorption's saturation in the quasi-cw four-wave mixing and with the inertia in the short pulse's regime is observed.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A review is given of the main works in the field of laser engineering and technology aimed at devising and using lasers in medicine, microelectronics, for treatment of materials, and in instrumentation.

A comparative analysis of effectiveness of two adaptive algorithms is carried out using the formalism of radiation transfertheory. It is shown, that under practically reasonable conditions, the method with pure amplitude adaptation provides better results both on energetic and far field angular parameters of the scheme, than that based on phase conjugation. The consideration is illustrated with a simple model situation. INTRODUCTIONRecently several adaptive schemes12 have been proposed for the reduction of laser beams' divergence caused by a refraction at a randomly disturbed water-air interface. The algorithms suppose the use of radiation, reflected by the boundary, as a source of information about its spatial structure. The main idea of the methods is to concentrate a signal wave to be transmitted at such quasi plane areas of the interface, where refraction deviations of light rays from their initial directions areminimal. This purpose is achieved via an adaptive control of the signal field. An angular filtration of reflected wave allows todetermine the localization of appropriate sections at the interface and it is a common feature of the schemes. They differ in away of transformation of the reflected field into signal one

A mathematical model of interaction between laser radiation and multilayer biological tissue has been developed. At a pulse duration shorter than 1 ms acoustic or shock waves are generated in the tissues simultaneously with a rapid temperature rise. At radiation power densities lower than approximately 109 W/cm2 in the absence of phase transition acoustic vibrations arise from thermal expansion of the heated volume.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The schemes of the coherent-image frequency conversion based on transmission and reflection dynamic gratings are studied. The effect of the processes of recording-waves energy exchange and absorption in a medium volume upon the diffraction efficiency of a reconstructing beam is investigated within the scope of a theory of four-wave mixing. Comparison with the case of degenerate four-wave mixing has been conducted and the possibility of the diffraction- efficiency improvement under the frequency shift of a reconstructing beam beyond the absorption band has been analyzed.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The paper deals with an adaptive system for collimated light beams transfer through a distorted interface of two media with nonequal refractive indexes (e.g., n and 1). The proposed method is based on real time searching for quasiplane parts of the boundary appropriate for the transmission of strictly directed beams without a significant increase of their divergence. The reflection of a probe field is used to locate these areas and to govern a signal beam formation procedure.

Institute of Physics, Academy of Sciences of Belarus,220072, Minsk, BelarusABSTRACTAn adaptive system for divergence reduction of optical radiation passing througha waved interface of two different media has been investigated. The proposed approachprovides one—way transfer of signal. The effectiveness of the method has been experi-mental ly confirmed.1. BASIC ALGORITHMThe collimated beams transfer through inhomogeneous media is a principal aim ofadaptive optics including wavefront conjugation (WFC)1,2 In conventional techniquesa light source emits a pilot beam from opposite side of medium in order to obtain theinformation about its distorting properties. It makes impossible the unidirectionallight beam transfer, i.e. beam divergence correction when no counterpropagating wave-front may be used. In the paper a method of light beam distortions reduction has be-en studied which overcomes the above mentioned difficulty when light field is aberra-ted by disturbed interface of two transparent media. Following that algorithm the wa-yes reflected from the interface are angularly selected and returned back by the WFC-mirror.This paper deals with another type of unidirectional adaptive system for thisproblem solution based on spatial light modulator (SLM) application. The modulatortransmission is controlled by the radiation reflected by the interface of two diffe-rent media and carrying the information about its spatial structure. The main idea ofthe method implies the signal light field concentration on those sections of interfa-ce, which are almost normal to the beam direction, and is illustrated by Fig. 1.At the first stage (Fig. la) a collimated pilot beam PB is directed parallel tothe axis of telescopic system L1-L2 to the boundary of external medium having a rela-tive index of refraction n. The objective L1 images the patching parts of illuminatedsurface onto the SLM plane T with those rays which are reflected back into the objec-tive L1 aperture. The aperture of objective and a diaphragm D in its focal plane se-lect the rays whose directions are close to the pilot beam axis thus picking up theareas of desired inclinations.At the second stage the signal beams SB of appropriate configuration are formedvia transmission through the illuminated parts of SLM. Due to optical conjugation ofthe plane T and disturbed interface the signal rays retrace the paths of pilot ones asit is shown in Fig. lb by wide line. This circumstance provides an essential advantageover the selective WFC method because in the latter case the signal beams penetrateinto the external medium along the reflected beams traces. This, under other condi-tions being equal, leads to the growth of the refracted radiation divergence. Not so-phisticated estimations show that the deviation angles of output signal rays in the

The results are reported of a theoretical analysis of resonatorless optical bistability of the WFC-mirror on the basis of degenerate four-wave mixing in a resonant medium. The conditions set on the fields and parameters of a nonlinear layer leading to an effective nonstationary energy exchange and to the appearance of resonatorless optical bistability are discussed.

A scheme for control of the transfer function of a nonlinear Fabry-Perot interferometer (F-P) using an independent light beam (optical pumping), tuned in frequency to the absorption band from the excited level of resonant medium, has been suggested. The possibility of switching operating modes of the interferometer (differential amplification, discriminator, optical bistability) has been shown.

The conditions of optical multistability in Fabry-Perot interferometer with a two-component resonant medium have been considered. The possibility for realization of the decaying and regular intensity pulsations of a light field has been shown and the conditions of such a realization have been analyzed.

A scheme for the realization of optical bistability in a nonlinear Fabry-Perot (F-P) interferometer has been considered under conditions of multifrequency excitation. The dependencies of the spectral-components intensities, their ratios, and the total intensity at F-P output on the input intensity have been analyzed. The possibility to realize the optical control of radiation color as perceived by the eye has been shown.

The light field is theoretically calculated, which is set up as the result of multiple reflections in a resonator, composed of phase-conjugate mirrors and nonabsorbing point-source hologram situated between them. On the basis of scattering matrix formalism the dependence of the field of reconstructed point sources upon reflectivities of phase-conjugate mirrors is investigated. The possibility to control the spatial structure of the internal field is shown.

The focused ion beam (FIB) miller allows preparation of site-specific transmission electron microscopy (TEM) specimens from a wide range of materials in both cross-sectional and planar configurations [1,2]. However, radiation damage during exposure to the high-energy gallium beam may result in the formation of amorphous regions on thin film specimens. The thickness of such damage layers, on both sides of a TEM specimen, is comparable with the thickness required for lattice imaging. For example, the thickness of an amorphous layer in Si after 30 kV Ga+FIB processing has been reported in the range from 15 [3] to 28 nm [4]. This problem limits the capabilities of FIB sample fabrication.The aim of this study was to investigate, in detail, the structure, composition and the thickness of the damage layers in Si specimens after milling with a gallium ion beam. Using a FEI xP200 FIB system, with 30 kV Ga+ions, a row of trenches on a silicon sample was milled under different beam currents ranging from 150 to 6600 pA. The average size of such trenches was 15×10 μm wide and 1 μm deep. The trenches were then removed from the FIB and sputter coated with a thick Au film to preserve the trench surfaces from further damage during subsequent TEM specimen preparation steps. Cross-sectional TEM specimens of the trench walls were then prepared using standard FIB procedures [5]. Observations were made using a Philips CM 200 Field Emission Gun TEM operating at an accelerating voltage of 200 kV.

Theoretical analysis of nonconventional schemes of four-wave mixing (FWM) using additional irradiation of resonance medium, which enables the realization of noncoherent optical control of the process efficiency, has been carried out. The possibility of significant increase in the phase conjugate reflectivity and decrease in the pump wave intensity, required for realization of optical bistability, has been shown. Optical control and intensification of FWM in Rhodamine 6G solution have been experimentally accomplished

In this paper a theory of a new holographic contouring method based on application of absorption medium is proposed, allowing definition of absolute surface relief.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Institute of Physics, BSSR Academy of Sciences,220602 Minsk, USSRI.V. Stashkevitch and A.V. ChaleyByelorussian State University, Department ofPhysics, Minsk, USSRABSTRACTNew devices for the parameter control of light beams based on thesystem "relief grating - liquid crystal" have been studied. It wasshown that the modulator, switched polarizer, deflector and bistabledevice based on such a system, possess several features that are notattainable in ordinary liquid crystal facilities.1. SYSTEM "RELIEF GRATING - LIQUID CRYSTAL"Electrooptical properties of liquid crystals (LC) have determinedtheir extensive use in different devices for optical processing andinformation display. Flat tube filled with oriented LC is an import-ant component in the majority of the devices (modulators, deflectors

The influence of magnetic field on the wave-front conjugation at degenerate four-wave mixing in resonant-absorbing atomic iodine va-pors has been studied theoretically. It is shown that depending on the magnitude and direction of the magnetic field, interacting waves pola-rization, as well as on the interaction length and intensity of pump waves, the conjugation efficiency can both increase and decrease. The greatest increase in the wave-front conjugation efficiency of radia-tion with a frequency corresponding to the line centre F =4- r =3 is attained in a transverse magnetic field with the interacting waves polarization orthogonal to the field.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.