The paper presents theoretical and experimental investigations of light beam self-trapping in a photorefractive
medium based on Plexiglas (polymethylmethacrylate, PMMA) with photosensitive phenanthrenequinone (PQ)-
molecules. It is shown that the self-trapping of a laser beam is generated due to the self-interaction of the propagating
light wave under the conditions of a well balanced concurrence of the effects of light diffraction and nonlinear focusing.
A new method for controlling the waveguide cross-section by changing the ratio of two competing mechanisms of the
nonlinear refractive-index variation (namely the formation of the photoproducts and the heating of the medium while
varying the power of the light beam) is proposed.
The recording of self-trapping structures implemented in PQ-PMMA layers has been realized with two laser sources
(405 nm and 514.5 nm) with an average power of several mW. It is shown that the photoattachment of the PQ-molecules
to the polymeric chains and the formation of the photoproduct play the decisive role for the light-induced increase of the
refractive index. Besides, the formation of the waveguide is strongly influenced by heating of the medium, which results
in an additional thermal defocusing of the light beam.
It has been established that the parameters of the waveguide (cross-section and length) are strongly dependent on the
wavelength and the power of the laser radiation, as well as on the concentration of the PQ-molecules. Waveguiding
structures with a diameter of 100 μm were recorded in samples with a high PQ-concentration (up to 4 mol.%) for the
wavelength of 514.5 nm. Reducing the dye-concentration by one order requires shorter (blue) wavelengths (405 nm).
The dependence of the waveguide parameters and the optimal laser wavelength on the concentration of PQ-molecules is
confirmed by the numerical calculation including a 3D-model of the light self-trapping.
In this work, optical propagation through turbid media is analyzed by FDTD simulation. In particular, the method is
applied to biological tissues. Continuous light propagation in turbid media has been widely studied, but pulsed light
propagation has received less interest due to its complexity. Therefore, in this work we focus on pulsed light. FDTD
method is applied to several media with optical parameters in the typical range of those observed in biological tissues.
We perform an analysis of the variations of pulsed light propagation as a function of the scatterers characteristics
(namely size, concentration, and optical contrast). The results are compared with those obtained by the use of the
diffusion approximation. The potential of the FDTD method over the diffusion model is given by its high accuracy, its
capacity to perform time-resolved simulations, and the fact that it carries all the information about the phase and
coherence of the wavefront. The results of this work can be applied to a wide range of areas of interest like the time-resolved
study of ultrashort light pulses propagation, the optimization of optical penetration depth, the coherence
properties of pulsed light, and the effect of modified wavefronts in light propagation.
Optical Phase Conjugation is a non-linear optical phenomenon that generates a phase conjugate replica of an incident
beam. It has been widely used to suppress the effects of aberrations in optical systems such as resonators or imagetransmitting
optical fibers. In this work, the possibility of using optical phase conjugation as a means of suppressing the
effect of scattering in turbid media is analyzed, with the final aim to apply it to biological tissues.
Firstly, light propagation through a slab representing a turbid sample was calculated by solving Maxwell's equations
with the Finite-Difference Time-Domain method, in order to preserve all the information about the phase and coherence
of the wavefront. The non-linear process that takes place within the phase conjugation mirror is described by coupledwave
theory. A set of simulations was performed, and the results confirm the feasibility of using this effect to
compensate the effect of scattering in turbid media.
Subsequently, an experimental set-up was performed. In order to obtain a phase conjugation mirror, degenerate fourwave
mixing was achieved by a real-time volume holography configuration. The pulsed laser source was a Nd3+:YAG
laser at its second-harmonic (532nm). An ethanol solution of Rhodamine 6G was used as a non-linear medium. A lipidbased
scattering sample was obtained by a solution of homogenized milk and distilled water, which provided us with an
appropriate tissue phantom. The experimental results demonstrate scattering suppression, and constitute some
preliminary measurements of an effect with a promising potential for a wide range of applications.
The paper presents an optical device that permits dynamic limiting of the power of nanosecond pulsed laser radiation.
Different possibilities to control the characteristics of optical limiters based on reverse saturable polymethine dyes with
the use of schemes including lenses and diaphragms have been analyzed. It is proposed to change the geometric position
of a dye cell relative to the focal region to control an operation threshold of the limiter. It is established that the
efficiency of optical limiting may be improved using additionally the effect of thermal defocusing.
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.
The reflection mechanisms are analyzed for the incoherent light beams interacting in a medium with thermal
nonlinearity. The propagation geometry of the light beams within a cell with absorbing organic dye is determined, and
the intensities of laser radiation associated with the nonlinear reflection effect are estimated. It is demonstrated that on
nonlinear reflection one can observe transformation of the spatial structure of a signal beam. The reflected light beam
occupies the region associated with the geometric reflection of the signal beam from the reference one. It is found that a
thermal lens formed when a laser is operating in the pulsed mode is transformed as a vertical thermal "plate" due to the
convection currents of the dye solution.
Optical techniques applied to biological tissue allow the development of new tools in medical praxis, either in tissue
characterization or treatment. Examples of the latter are Photodynamic Therapy (PDT) or Low Intensity Laser Treatment
(LILT), and also a promising technique called thermotherapy, that tries to control temperature increase in a pathological
tissue in order to reduce or even eliminate pathological effects. The application of thermotherapy requires a previous
analysis in order to avoid collateral damage to the patient, and also to choose the appropriate optical source parameters.
Among different implementations of opto-thermal models, the one we use consists of a three dimensional Beer-Lambert
law for the optical part, and a bio-heat equation, that models heat transference, conduction, convection, radiation, blood
perfusion and vaporization, solved via a numerical spatial-temporal explicit finite difference approach, for the thermal
part. The usual drawback of the numerical method of the thermal model is that convergence constraints make spatial and
temporal steps very small, with the natural consequence of slow processing. In this work, a new algorithm
implementation is used for the bio-heat equation solution, in such a way that the simulation time decreases considerably.
Thermal damage based on the Arrhenius integral damage is also considered.
Nowadays, all optical devices based on nonlinear effects acquire a great importance in optical communications systems
and photonic processing. Particularly relevant are the devices that use low-level power pumping in the generation of
those effects. These optical devices can be implemented by means of different structures and materials. One of the most
significant structure, here described and presented, is the semiconductor semimagnetic microcavity, composed by a
Fabry-Perot microcavity with a semiconductor semimagnetic material and a quantum well in the middle. Inside these
media nonlinear effects such as four wave mixing and magneto-optical polarisation rotations can be observed and
utilised for developing optical amplifiers, wavelength converters and nonlinear magneto-optical based devices. In order
to reduce the pumping power needed for obtaining nonlinear effects new structures with different materials can be built.
For instance, Fabry-Perot vertical microcavities, whispering gallery based microcavities or hybrid system of photonic
crystal microcavities can improve their performance and so make possible a real implementation. A key point in the
design of such micro-resonators is the election of the appropriate material inside. A study of the influence of several
materials, with a high dispersion and able to provoke electromagnetically induced transparency is, also, presented. The
changes of the quality factor of these nonlinear micro-resonators are analysed. Potential applications for optical
computing are shown.
This paper is devoted to growth and doping of semiconductor photorefractive cadmium telluride (CdTe) crystals as well as to the investigation into their spectroscopic and non-linear optical properties. The crystals are doped with vanadium, iron, and titanium. Two methods have been used for the production of doped crystals: diffused post-growth doping and growth of doped crystals from melt. Non-linear optical properties of the samples were studied at a wavelength of 1.06 μm for a four-wave mixing geometry and 1.54 μm for a two beam coupling. Maximum 2% diffraction efficiency at 1.06 μm was revealed with the convergence angle of light beams approximating 8" for the grating period of 7 μm. In this case the dynamic grating lifetime was found to be about 0.2 μs. Under beam coupling at ~ 1.5 μm, the conditions of maximum gain (0.7 cm-1) were observed in the experiment for a minimum grating period of 1 μm; and the gain could be slightly enhanced by application of a dc electric field (~ 2 kV/cm) up to 40%.
The methods for the optical signal conversion based on the optoelectronic system "relief grating - liquid crystal" and liquid-crystal (LC) cells using S- or twist-effect have been presented. New schemes forming the basis for realization of bistable LC devices, optoelectronic logic elements and systems of electrically-coupled LC elements intended for the production of laser oscillations at the constant input intensity have been proposed. It has been demonstrated that with the use of varying parameters of optoelectronic feedback one is enabled to set up both regular and chaotic intensity oscillations, to control the frequency and form of these oscillations, to realize functional changes of logic elements. The
developed LC systems have been introduced into the educational practice of students mastering modem information techniques.
We demonstrate a possibility to write efficient and thermally stable volume holographic gratings in a glassy polymer material based on PMMA and phenanthrenequinone with layers prepared by casting the liquid solution of ingredients on a substrate and drying to a solid state. A high concentration of phenanthrenequinone (up to 4 mol.%) makes it possible to use photosensitive layers of lower thicknesses (50 - 180 μm) for the recording of efficient holographic gratings. The exposing is followed by a thermal amplification of the grating due to diffusion of residual phenanthrenequinone molecules and fixation by an incoherent optical illumination. We present experimental temporal curves of the refractive index modulation and diffraction efficiency both under the exposure and the heating process. The behavior of the gratings under temperatures up to 140°C has been studied.
The schemes of degenerate and nondegenerate multiwave mixing in saturable absorbers (Rhodamine 6G and polymethine 3274 U dyes) exhibiting higher-order nonlinearities have been analyzed experimentally. The role of polarization gratings resultant from spatial modulation of the light field polarization state at the orthogonal polarization of the hologram recording waves has been established. Also, it has been found that polarization of the diffracted wave is dependent on the diffraction order. The frequency conversion of coherent images from infrared to the visible and
between different wavelengths of the visible region has been realized experimentally.
The schemes for nonlinear recording of dynamic holograms in multilevel resonant media, in conditions when the fifth- and
higher-order nonlinearities are exhibited, have been studied both theoretically and experimentally. The optical methods to control the diffraction efficiency of nonlinear dynamic holograms with the use of an additional light beam tuned out into the absorption band from the ground or excited state of the molecules have been considered.
The energy efficiency of multiwave mixing and geometrical parameters of spatial solitons in photorefractive Bi12TiO20 crystals in conditions of pulsed and continuous-wave laser excitation have been studied experimentally. It has been found that with the use of 532 nm-wavelength laser pulses switching of the photorefractive nonlinearity mechanism requires a time interval in excess of 20 - 50 ns. And saturation is observed when the duration is over 100 ns. The formation dynamics of spatial solitons in photorefractive Bi12TiO20 crystals has been analyzed using radiation of a continuous-wave He-Ne laser. It has been determined that the formation conditions and dynamics are influenced by a number of factors including the radiation input geometry of a crystal, power of the light beam, orientation of its polarization relative to the crystal axes, applied electric field and its direction.
The results of theoretical and experimental investigations into degenerate and non-degenerate four-wave mixing in Fabry-Perot microresonator with dye solution as a nonlinear medium are presented. It is shown that the efficiency of holographic methods for wave-front and frequency conversion may be considerably increased due to the use of recording of dynamic holograms in nonlinear interferometers. Spatial-temporal transformation of light beams for different configurations of interaction has been performed and the methods for control of energy efficiency of intracavity dynamics gratings are discussed.
The laboratory works are meant to train the university students mastering modem information technologies and techniques based on optical data transmission and processing. These works involve the use of fiberoptic systems and transmission methods for optical signals. Students study the operation principles of fiberoptic communication and processing systems, optoelectronic components, one- and multimode fibers, optical input/output couplers, multiplexers, optical dividers and connectors.
Advances in the development of nonlinear interference and holographic systems based on four-wave mixing point to great potentialities of these systems for real-time processing and correction of the light fields, formation of the desired space-time structures of laser radiation, image transfer, realization of logic and mathematical operations, creation of bistable devices and adaptive optics elements. This work presents the results of theoretical and experimental studies into the processes of light field transformations upon frequency-nondegenerate four-wave mixing in nonlinear Fabry-Perot interferometer. The principal aim is to develop a theory of intracavity four-wave 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 characteristics of light beams. For theoretical description of typical experimental situations we used the round-trip model of interferometer adapted for the geometry of four-wave mixing, which can be realized in the scheme of symmetrical oblique incidence of reference and signal beams to the front and back mirrors of cavity. The conditions of magnification of dynamic gratings efficiency due to contribution from multiple interference of reading light beams have been studied experimentally and by means of theoretical modeling.
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 - 1th-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 %.
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.
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).
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.
Efficient and thermally stable volume holographic gratings in glassy polymeric material based on PMMA and phenanthrenequinone have been recorded. Photosensitive layers were prepared by casting the liquid solution of ingredients on a substrate and drying to a solid state followed by a separation of the polymeric film. This technique was applied to create a possibility to write highly slanted gratings between prisms and to stick them to lightguides with glue. High diffractive efficiencies and moderate angle selectivity of the gratings were reached due to a high concentration of phenanthrenequinone (up to 4 mol.%) making it possible to use the photosensitive layers of lower thicknesses (60 - 150 μm) for the recording of the efficient holographic gratings. The exposing is followed by thermal amplification of the grating due to diffusion of unreacted phenanthrenequinone molecules and fixation by an incoherent optical illumination. The processes of generation, amplification and fixation are discussed for holographic gratings. The holographic gratings were written with an Ar-laser (wavelength 514,5 nm). The grating amplification was realized by heating up of the sample to 50-85°C.
The importance of nonlinear optical devices is increasing due to their hopeful characteristics such as small size, high speed or even low power consumption. These devices integrated in all-optical systems achieve the best results because of the elimination of optoelectronic or electro optic conversions that imply great reductions in these advantages. Therefore the main effort should be directed to make as many functions as possible by optical means. Among these functions, wavelength conversion or amplification seem to be likely to implement with a nonlinear device. In this work a structure called Semiconductor Semimagnetic Microcavity (SSM), for optical amplification and wavelength conversion, is introduced and studied. This study requires a suitable method for nonlinear series devices. It must take into account each wave and its relationship with the others. An Extended Yeh matrix is appropriate for the characterization of this structure. The method reveals that if the microcavity is exposed to an input signal and a pumping input signal and also matches the conditions of degenerate four-wave mixing, another wave at a different wavelength appears. What is more, the original input signal becomes greatly amplified depending on the pumping input signal. The process of obtaining these results with the Extended Yeh matrix applied to a SSM is shown. Optical wavelength conversion and optical amplification in a microcavity is demonstrated by means of this matricial method.
The potentialities of diffraction methods for wavefront transformations may be considerably widened due to the use of nonlinear recording of dynamic holograms enabling multiwave mixing in media with the fifth and higher order nonlinearities. There is a great variety of such media including the resonant ones for which the presence of higher order nonlinearities is conditioned by the absorption saturation effect and transitions between different excited states of the molecules. However, in the majority of previous studies of multiwave mixing the resonant medium approximation has been used disregarding the induced anisotropy effect. This work presents a theoretical model and experimental studies of the energy efficiency of multiwave mixing in complex molecular media exhibiting higher order nonlinearities, in two cases: when the nonlinear cavity is introduced in the Fabry-Perot interferometer (IFP), and without it. Owing to the use of different combinations of mutually aligning polarizations for interacting waves, one is enabled to determine the contribution into the interaction efficiency by various dynamic gratings and nonlinearity mechanisms. The role of polarization gratings resultant from spatial modulation of the light field polarization state at the orthogonal polarization of the hologram recording waves has been established. Comparisons between the contributions of the above gratings and “normal” gratings recorded by identically polarized light beams into the process of multiwave mixing have demonstrated that the relation of these contributions is dependent on the intensity of interacting waves, and also it has been found that polarization of the diffracted wave is dependent on the diffraction order.
In this work a theoretical study of the interaction between a light beam and an anisotropic nonlinear interferometer has been considered and methods to control the transmission of the microcavity using optical and magnetic fields have been developed. It has been demonstrated that anisotrophy of intracavity media determines the differences in transmission functions for various polarization modes and produces polarization instability. Varying spectroscopic parameters of the resonant medium and parameters of the anisotropic element, different types of intensity self-oscillations for different polarization modes can be obtained. To control the characteristics of nonlinear interferometer, it is proposed to use an additional light beam whose frequency is tuned into the absorption band from the excited level. The propagation characteristics of periodic magento-optical and dielectric multilayer films made of alternating layers of these materials having a symmetric periodicity with the center of the structure under a magnetic field is analyzed. The magnetic induction on this type of materials is temperature dependent and modifies the transmission and reflection characteristics of these structures. This kinds of structures, gives us the possibilities for an additional controlling of the characteristics of nonlinear interferometer.
The surface relieves shaped in processes of thermoannealing of exposed polymer layers containing photosensitive admixtures are investigated. Several ways of resolving ability improvement of the relief recording are proposed and implemented experimentally. They are based on: (1) retardation of deformation reate, (2) depression of glass transition temperature of a polymeric matrix, (3) considerable increase of annealing temperature of the samples and (4) overlapping of the recording and thermal developing processes under photorelief shaping by one laser pulse. The last method has made it possible to record surface gratings with spatial frequencies in the limits of 50-1500 mm-1.
A laboratory bench has been developed and a laboratory manual has been prepared for the practical course in optical data processing including the following laboratory exercises: “Spatial Filtering of Images”, “Optical Bistability”, “Intensity Self-Oscillations and Optical Chaos”, “Logic Optical Elements”. These laboratory exercises enable the students to study the analog and digital information conversion methods and the effects underlying them. The laboratory bench was created on the basis of the electrically controlled liquid-crystal elements and involved a computerized recording system for temporal and spatial characteristics of light beams.
The dynamics of orthogonal polarization modes in anisotropic plane resonators with resonant medium has been studied. A model of light-induced anisotropic effects in a resonant medium under polarized excitation in conditions of strong saturation has been developed. The origination conditions of polarization instability and its influence on spatial-temporal dynamics have been determined. The methods of arranging the laser beams with special polarization structure have been suggested.
In the present work consideration is given to theoretical and experimental analysis of the possibilities for improving the efficiency of multiwave mixing in the process of dynamic hologram recording in solutions of complex organic compounds with additional irradiation of resonant medium at a frequency falling within the absorption band from the excited level. Three- and seven-fold increase in the diffraction efficiency has been realized in Rhodamine 6G dye for four- and six-wave missing, respectively.
Investigation of nonlinear interferometers symmetrically pumped by two light beams has been proposed. An analysis of the conditions for realization of symmetrical and asymmetrical optical bistability, different spatial-temporal structures due to symmetry breaking bifurcation has been performed.
We report new theoretical results on polarization effects within pump-probe scheme of interaction in polarization inhomogeneous media. Our findings are applicable to explanation of experimental data on combustion diagnostics as well as for optimization of polarization geometry conditions under saturation regime.
In the work consideration was given to investigation into the spectroscopic and nonlinear optical properties of photorefractive semiconductor cadmium telluride crystals doped with vanadium, ferrum and titanium. Introduction of dopants was required to produce an impurity absorption band in the near IR region and enhance the photorefractive properties. Two methods have been used for the production of doped crystals: diffused post-growth doping and growth of doped crystals from melt. Nonlinear optical properties of samples were studied at the wavelength of 1.06 micrometer in a four-wave mixing scheme. Maximum diffraction efficiency was revealed for the convergence angle of light beams approximating 8 degree, with the grating period of 7 micrometer and was equal to 2%. The dynamic grating lifetime was about 0.2 microseconds.
The schemes of light beam transformations by volume dynamic holograms in resonant media revealing the fifth- or higher- order nonlinearities have been theoretically analyzed. N- wave mixing has been realized by changing of the propagation direction or read-out wave frequency in the solution of Rhodamine-6J dye and polymethine dye 3274U. It has been demonstrated that the experimental result are in good agreement with the theoretical data obtained for a three- level medium model with due regard to absorption form the excited singlet level.
We consider the dynamics of a nonlinear Fabry-Perot interferometer symmetrically pumped by two light beam. An analysis of the conditions for realization of symmetric and asymmetric modes of optical bi- and multistability has been performed using a theory of degenerate four-wave mixing adapted to a Fabry-Perot resonator with amplitude-phase nonlinearity. Complexity of the dynamic behavior due to symmetry breaking bifurcations has been investigated both theoretically and numerically.
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.
Conversion of light beams by the dynamic volume holograms in resonant media revealing the fifth- and higher-order nonlinearities has been analyzed. The experimental results on the energy and angular characteristics of laser radiation diffracted from a dynamic transmission grating in the solution of Rhodamine 6J dye and polymethine dye 3274U are considered. A theoretical model that allows for the calculation of the energy efficiency of light-beam conversion at different propagation directions of a reconstructing wave has been proposed.
For the purpose of determining the higher-order nonlinear optical susceptibility the diffraction method based on investigation into the Fourier-expansion spatial components for the anharmonic grating of a refractive index has been used. Condition of the second-order Bragg diffraction is satisfied through doubling of the recording-wave frequency. This variant of diffraction method has been theoretically studied for the resonant media modeled by three- and four- level schemes taking into consideration the transitions between the molecular excited states. Experimentally, the method proposed for measurements of the higher order nonlinearities has been realized with the use of the six- wave mixing of monopulse YAG laser radiation in the solution of polymethine dye.
The possibility of using liquid-crystal elements, based on the S-effect and operating as multifunctional optoelectronic devices, for optical data processing system has been demonstrated. Several logical operations and modes of optical bistability, differential amplification and light- pulse generation have been realized.
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.
KEYWORDS: Holograms, Phase conjugation, Diffraction, Four wave mixing, Absorbance, Energy efficiency, Information operations, Absorption, Spectroscopy, Frequency conversion
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.
KEYWORDS: Holograms, Absorption, Four wave mixing, Absorbance, Diffraction, Frequency conversion, Image restoration, Energy efficiency, Volume holography, Optical signal processing
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.
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.
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.
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
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