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.
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.
In the work the approximate analytical relations describing the director distribution in depth of a plane-parallel layer of nematic liquid crystal are presented. The analytical expression determining the orientational effect of the periodic surface in a system "relief grating - liquid crystal" is derived. Its diffraction characteristics are studied theoretically. Relaxation kinetics of the director in a plane-parallel layer of nematic liquid crystal is considered taking account of the microscopic inertia moment.
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.
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.
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.
In the work the effect of orientational inhomogeneity of nematic liquid crystals (NLC) on characteristics of diffraction optical elements (DOE), based on the system relief grating-liquid crystal, was considered. The analytical solution for the NLC director and refractive index spatial distribution has been obtained and the diffraction efficiency of the system relief grating-liquid crystal has been calculated for different diffraction orders. As a result, it has been found that inhomogeneous orientation of NLC leads to considerable variation of the diffraction efficiency across the DOE area.
In the work consideration is being given to inhomogeneity of LC orientation at the profiled-surface relief gratings. Its effect on the diffraction characteristics of gratings is analyzed. It is demonstrated that for switchable diffraction elements with LC this effect may be neglected in quite a number of cases.
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.
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