Our previous investigation regarding liquid crystal mixtures, used as a medium for dynamic holography, has proved the influence of addition of PVK (polivinylocarbazol) layer to the LC cell structure as a sensitivity amplifier [1]. This modification was very useful for bettering the dynamic properties of these modulators. In some cases (of LC Cells) we observe some kind of memory effect - holograms written before could be observed months after writing. We decided to examine different cells to determine CL Cell construction as rewritable holographic media.
The possibility of diffraction pattern generation in LC (Liquid Crystal) cells working as a dynamic write-read media was proven. Recording of holographic gratings formed by interfered He-Ne laser beams onto LC-cells with pure and dye-doped mixture have been investigated. The possibility of optoelectronic reconstruction of digitally stored microinterferograms allow us to adopt them in multimedia application. The hologram of virtual or real object was reconstructed by coherent illumination of optically addressed spatial light modulator (OASLM) containing holographic grating. The results obtained from LC cells of standard twisted nematic type were examined. As a result of examination of physical properties of nematic-type liquid crystal mixtures, new method of realization of LC cells were proposed. The experimental results of replacing TN cells with polivinylcarbazole (PVK) photosensitive layer cells have been discussed.
In the paper a new approach to quasi real-time phase reconstruction of digitally recorded holograms is presented. A new, low cost and fast measurement system based on digital holographic interferometry is described. Examples of experimental results representing deformations of an object under thermal load are shown.
This paper presents theoretical considerations on recording and reconstruction processes of sum- and product-type multiexposure digital holograms in coherent and incoherent configuration. The analysis of the result from the point of view of digital holovideo application is performed. The method of optoelectronic reconstruction of digitally stored holograms is presented.
KEYWORDS: Digital holography, Holograms, LCDs, Liquid crystals, Optoelectronics, 3D image reconstruction, Holography, Charge-coupled devices, Digital micromirror devices, Digital recording
Recent advances in high-resolution CCD detectors allow the development of the concept of digital holography that relies on capturing of 2D microinterferograms and their further numerical reconstruction. This approach is valid for optical metrology applications as it gives direct access to the phase and intensity of an object at the selected distance `d'. However it is not convenient for direct 3D display purpose. It is the reason why the authors propose the optoelectronic reconstruction of a hologram that is digitally recorded and transferred to another optoelectronic medium. The application of LCD matrices and optically addressed liquid crystal cells as reconstruction medium are discussed. Their applicability for computer generated and optical holograms is tested by means of simple experiments. The problems connected with limited resolution of the recording (CCD) and reconstruction (LCD, DMD) devices are considered. The comparison of the results obtained by numerical and optoelectronic means are presented, together with a discussion of the limitations and further possibilities of these techniques.
The progress in high resolution CCD detector technology provides the electronic medium for digital registration of holograms. This possibility is widely used in digital holography, which allows reconstruction of numerically stored microinterferogram. This approach is very useful for optical metrology application, however it is not convenient to real time visualization of 3D object reconstruction. In the paper we propose to use only the stage of digital registration and then transfer these data to LCD matrix to form an optoelectronic version of microinterferogram. This hologram is reconstructed optically by a laser beam, giving possibility to visualize an amplitude-phase object's image. These procedures together with fast LCD and proper optical imaging system should enable to produce digital holographic films.
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