Liquid crystal displays in different modes are suitable due to their birefringence properties and wide transmission range. The paper discussed advantages amplitude-phase modulators and focused on boundary conditions for the application in digital holography (generation of 3D light wave) and for dynamic pattern generation. Implementation demands are discussed on the example of an optical system for parallel recording and optical reconstruction of digital hologram. Optical methods based on digital holography are highly effective for diffractive element synthesis. Modern production of
digital hologram is characterized by high degree of flexibility and complexity. According to this the use of proposed method is useful for designing and developing an optical system able not only for fringe pattern fabric structures but as well to allow more complex pattern including singular for image forming. We report on a method for synthesis of digital holograms taken with interference of laser beams diffracted on a spatial light modulator. The proposed technique for modeling of adaptive diffractive elements computes the propagation of the complex optical wavefront diffracted by the
object and used to determine the needed spatial light modulator (SLM) pattern. The extension of new method of modeling diffraction on amplitude-phase mask and possibilities of its practical application such as computer modeling of diffraction on a SLM, which consists of squared cells, for a wavefront reconstruction are considered. Conclusions regarding the possibilities the representation the arbitrary fields by using the discrete matrix of elementary diffractive aperture cell for enhancement of iteration algorithm of hologram synthesis and phase retrieval are arrived at. Proposed
method for computer-generated holograms (CGH) enables one to synthesize CGH's and simulate digital image processing techniques for 3D image reconstruction. The process does not contain any Fourier transform calculations, and can thus be performed directly by grating recorder in line with recording. Nowadays miniaturized CCD and recent
successes in optical spatial light modulator system devices allow building compact digital holographic system. Combining the original dot-matrix method with interferometric image forming allows obtaining new visual effects for hologram or diffractive elements synthesis. The new approach in this project is the idea of using the optical interference field is recorded at the same time in different areas to give multiple grating. Thus the image cell that are written are not
separated into discrete dots of diffraction grating, like conventional dot-matrix spots, but form a continuous recording over relatively large area. Some advantages are that the basic cell, or pixel, is composed of not only a set of diffraction grating with various spatial frequencies but also may contain arbitrary pattern form and contain the hidden image or coding visual information. The result obtained by numerical and experimental means are presented together with a discussion of the limitations and further possibilities of this method.
KEYWORDS: Holograms, Image compression, Diffraction, Computer generated holography, Holography, Digital holography, 3D image reconstruction, Image restoration, Chemical elements, Digital imaging
The methods of increase the protective properties of holographic elements by using hidden image are discussed. The extension of the new method of wave equation solution is useful for providing analytical studying and numerical modeling of diffraction on amplitude-phase discrete mask. Possibilities of its practical application for structured light beam generation and wavefront reconstruction is considered. Conclusions regarding the possibilities of the representation of the arbitrary fields by using the discrete matrix of elementary diffractive aperture cells for an enhancement of the iteration algorithm of hologram synthesis are obtained. The method proposed of computer-generated holograms (CGH) synthesis enables one to synthesize CGH's and to simulate the digital image processing techniques for hidden image coding. The further improvement of this approach of coding amplitude-phase masks for both recording and reading of hidden image by holographic security devices is proposed. By using coding phase mask with quasi-stochastic distribution for diffraction pattern writing as additional structure on the protective hologram are explained. It is shown that computer generated hologram (CGH) can restore spatial structure represented by optical singularities. The conditions of reconstruction of the hidden image are discussed in case of encoding and decoding masks are not coinciding. A structure of a system that looks promising to produce a like hologram and method of operation directly images a pattern, which is previously calculated by computer and displayed on the amplitude-phase mask is explained. The results obtained by numerical and experimental means are accompanied with a discussion about extents of this method.
Each hologram: optical, digital and computer generated represents the phase and amplitude of an object. Therefore the process of object reconstruction may rely on one of two alternative procedures: optoelectronic direct reconstruction of hologram, which is represented by diffractive structure intensity, and recombining of object phase and amplitude as calculated from wavefront propagation process (here the method is based on singular wave component that is derived from a rigorous Sommerfeld's solution) or numerical reconstruction of digital hologram. In the paper we present the comparison of these two ways of optoelectronic reconstruction. The pros and cons for application of these procedures from image quality point of view are given. The experimental systems based on a Twyman-Green interferometer with two phase and amplitude LCOS or on a single digital hologram or computer generated hologram reconstruction setup are presented. The conclusions of these experiments will be utilized for optimizing of the process of production of security holograms with use of LCOS modulators.
A series of novel chiral azodye homo- and copolymers has been investigated for applications in optical data processing and display technology. Supramolecular chirality in those systems due to
helical superstructure leads to specific photo-optical response to circularly polarized light and, therefore, for creation of advanced photorecording media, especially for polarization holography.
Highly twisted smectic-like mesophases of side chain homo- and copolymers (short pitch TGB A* phase) appear visually transparent and optically isotropic but possess a hidden liquid crystalline
ordering, giving rise to rewriteable photorecording in relatively thick polymer films with high photoinduced phase retardation and diffraction efficiency. The amplitude gratings were written in polymer films with linearly polarized light but the phase gratings with circularly polarized light. Evolution of the photoinduced birefringence and diffraction efficiency, η1, is studied. For some polymers, polarization gratings are obtained with η1 value above 30%; overmodulation effects of the grating recording are observed and discussed. The effect of dark self-amplification is reported.
It was proposed technique for modeling of adaptive diffractive elements in holographic system that based on a new method of wave equation solution analysis of the aperture diffraction problem. The method is based on new integral approach to modeling of laser beam diffraction on an arbitrary aperture by investigation of the singular wave component derived from a rigorous Sommerfeld's solution. Developed on the basis of proposed integral representation the effective algorithm is useful for providing analytical studying and numerical modeling the aperture diffracted field without paraxial approximation and the specific form of the convolution kernel that describes the diffraction with taking into account the size of cell allows alternative reconstruction procedure of diffraction pattern. The structure of the diffraction field not only in far zone but also in near and middle diffraction zone depending on profile of the amplitude-phase diffractive grating can be analysed. The extension of new method of modeling diffraction on amplitude-phase mask and possibilities of its practical application such as computer modeling of diffraction on a spatial light modulator (SLM), which consists of squared cells, for a wavefront reconstruction are considered. Conclusions regarding the possibilities the representation the arbitrary fields by using the discrete matrix of elementary diffractive aperture cell for enhancement of iteration algorithm of hologram synthesis and phase retrieval are arrived at. Proposed method for reconstructed images of computer-generated holograms (CGH) enables one to synthesize CGH's and simulate digital image processing techniques for 3D image reconstruction by kinoform. The result of computer simulations and optical experiments are presented.
The possibility of using a new method of the wave equation solution for computer modeling of diffraction on a liquid crystal amplitude phase mask, which consists of squared cell, for a wavefront reconstruction, structured light beam generation and image composition was considered. The method is based on a new integral approach to modeling the plane wave diffraction on an arbitrary two dimensional aperture by investigation of the singular wave component as informative part of diffraction field. It was shown that the result of diffraction on arbitrary aperture being treated as a discrete sum of elementary unit cell waves and diffracted field can be presented via orthogonal wave functions that play a role of eigenmodes as plane waves in free space. Developed on the basis of proposed integral representation the effective algorithm is useful for providing analytical studying and numerical modeling the aperture diffracted field and allows eliciting features of spatial behavior. The specific form of the convolution kernel that describes the diffraction with taking into account the size of cell allows alternative reconstruction procedure of a diffraction pattern. Application of new procedure to practical diffraction related phenomena may improve the processing efficiency without creating any artifacts associated with the diffraction field. The extension of new method of modeling diffraction on liquid crystal panel and possibilities of its practical application to information display are considered. The result of theoretical study and computer modeling the diffraction on a discrete matrix of square elements in near field with Unit Cell Wave concept applied to arbitrary surface description was represented. Conclusions regarding the possibilities to represent the arbitrary fields by using the discrete matrix of squared cells are arrived at. The technique for optical coding an adaptive optical hidden image in holographic elements has been proposed. A structure of a system that seems promising to produce a like hologram and method of operation directly images a pattern, which is previously calculated using a computer and displayed on the liquid crystal panel was explained. It was discussed the method of complex amplitude phase field distribution modeling in screen plane for three-DI scene synthesis as well as capabilities and characteristics of amplitude phase liquid crystal display for dynamic image visualization by using the "wavegram". This technique and algorithm for an aperture - synthesized image of three-dimensional objects can be applied to holographic screen technology development, which may have ever-growing use in many applied areas of systems for three-dimensional information visualization.
It was discussed the using multi-frequency YAG:Nd infrared laser for long range non-destructive acoustic vibration measuring system for structural modal analysis. It was shown both theoretically and experimentally that a coherent function of a laser with acousto-optic device has an oscillations with the period depending on a laser cavity length and a number of resonator modes. The advantages of using the acousto-optic devices in a tandem scheme were discussed. The adjustment of such system due to on-axis shift is suitable for object selection. It was shown that the coherence function has optimal form for selecting a transparent object on light beam trace and optical delay line for semiconductor laser with short resonator can tune on maximum of coherent function at long distance. Accordingly the mutli-frequency laser can be used in heterodyne optical scheme instead of more costly stable one-frequency laser. A simple scheme of velocity measuring based on a semiconductive two-mode laser was proposed. Conclusions regarding the possibility using the resonator with acousto-optic device inside with a frequency chirp beam using for interferometer phase modulation measure system are arrived at. The application of a frequency-shifted laser beam to practical optical measuring system may improve the processing efficiency without additional adjustments.
The theoretical analysis and experimental results of this report illustrate the possibility of describing of diffraction phenomena using the objects and methods, which were developed in singular optics. The aperture-diffracted field can be represented as superposition of real physically existing waves: an ordinary wave component with an amplitude half that of the incident wave, and a wave component possessing a singularity. The investigation of the singular wave component as informative part of diffraction field is an important new trend. It was shown that a system of hidden dislocation lines composes the skeleton and represents the diffraction field topology. The analysis of topology of the diffraction field in case of plane wave diffraction on a slit was performed. The proposed experimental proof ground can be useful for studying the system of linear edge dislocations space evolution and properties, such as nucleation and annihilation, edge and mixed edge-screw transition.
For the first time it can be shown, experimentally and theoretically, that the field of plane wave, which diffracted on the perfectly conducted half plane (Sommerfield's solution), is presented as a superposition of the half amplitude source wave and wave, which contains edge dislocation that is formed on the screen border and described by the complex Fresnel integral. These two waves are real waves, unlike traditional representation as sum geometric and boundary waves, and as we have shown, can be split and investigated experimentally. On basis of this new representation the problem of diffraction arbitrary beam on the perfectly conducted half plane was solved. It was shown (theoretically and experimentally) that a diffracted beam is presented as a sum of the source beam half amplitude and a beam contains edge dislocation that is caused by the border of the screen.
It was shown that the well-known Sommerfeld's solution of the problem of a plane wave diffraction on a perfectly conductive half-plane screen can be expressed as a superposition of two waves, one being a plane wave with the amplitude twice smaller than the incident wave amplitude, and the other infinite-aperture wave with infinitely- extended edge dislocation. On the contrary with traditional components of the diffraction field, these wave can exist and propagate in free space separately with self-similar features.
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