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The multiplexed storage of permanent and real-time holograms in photorefractive BSO for use in image processing and spatial light modulation
No full textMultiplexed storage of permanent and real-time holograms in photorefractive BSO
No full textIn this paper we present a technique for storing holograms in crystals of bismuth silicon oxide (BSO) that combines reversible photochromic effects with the more usual real-time photorefractive characteristics. Photochromic effects have been observed before in these sillenite crystals but have generally been considered as a problem rather than as a possible mechanism for holographic storage. As the normal photorefractive (PR) behaviour is unaffected, however, simultaneous spatial multiplexing of both photorefractive (real-time) and photochromic (permanent) holograms is possible in the same crystal volume.We have demonstrated a number of applications here ranging from image synthesis to holographic interferometry. These operations are mostly based on the inherently separate nature of these two holographic gratings which can lead to relative phase shifts between the two simultaneously scattered fields by shifting the real-time grating with respect to the permanent one, using optical techniques. Furthermore, the permanent holograms also show unexpected dynamic behaviour in which a fast increase in diffraction efficiency is observed upon illumination by a beam at the highly absorbed blue wavelengths. This effect can be used for all-optical switching
Multiplexed permanent and real-time holographic recording in photorefractive BSO
No full textWe report permanent hologram recording in crystals of photorefractive bismuth silicon oxide (BSO) using reversible photochromic effects. At a recording wavelength of 488 nm, exposures of several minutes produce areas of faint discolouration in which the permanent hologram is stored. The normal photorefractive behaviour is unaffected however, permitting spatial multiplexing of both real time and permanent holograms. Experimental results and characteristics of this permanent recording in combination with the photorefractive process are presented
The multiplexed storage of permanent and real-time holograms in photorefractive BSO for use in image processing and spatial light modulation
No full textSpatial light modulation via enhanced diffraction efficiency of photochromic gratings in photorefractive BSO
No full textIn recent years, optical time-domain reflectometry (OTDR) has progressed from a laboratory experiment to a technique in everyday use by manufacturers and users of optical fibres. The principal attraction of the technique is its ability to give, non destructively, a good indication of the fibre-loss uniformity and therefore to reveal any localised defects in the fibre. It has also been employed as a means of measuring accurately fibre and splice losses, and of studying the longitudinal variation of fibre parameters
Applications of multiplexed real time and permanent holographic recording in photorefractive BSO
No full textPhotochromic effects in crystals of photorefractive bismuth silicon oxide have been used for the recording of permanent holograms. The combination of this permanent recording with the usual photorefractive real time recording has revealed some novel techniques in information processing and interferometry. These are based on the possibilities of multiplexing two distinct holographic gratings having identical grating wave vectors within the same crystal volume. Techniques ranging from image synthesis and logic operations to holographic interferometry and all-optical switching are demonstrated
Multiplexed storage of permanent and real time holograms in photorefractive bismuth silicon oxide for use in image processing and spatial light modulation
No full textWe present a technique for storing holograms in crystals of bismuth silicon oxide (BSO) that combines reversible photochromic effects with the more usual real time photorefractive characteristics. Photochromic effects have been observed before in these sillenite crystals but have generally been considered a problem rather than a possible mechanism for holographic storage. As the normal photorefractive (PR) behavior is unaffected, however, simultaneous spatial multiplexing of both photorefractive (real time) and photochromic (permanent) holograms is possible in the same crystal volume
Mechanism of photorefractive enhancement of photochromic gratings in BSO - Experimental results and phenomenological modelling
No full textWe report an increase of more than a factor of 100 in the diffraction efficiency from photochromic gratings written in BSO by uniformly illuminating these gratings with 488 nm light to induce secondary photorefractive gratings. Upon application of an electric field, the phase shift between the two gratings can he varied and under appropriate conditions the diffraction efficiency can increase. The dependence of the enhanced diffraction efficiency as a function of the applied electric field and readout beam polarisation was experimentally investigated for two different crystal orientations. Phenomenological modelling is presented requiring modifications to the phase angle between the photochromic and induced photorefractive gratings in order to reproduce the experimentally observed asymmetry in the increase in the diffraction efficiency. This suggests a periodic modulation of the photorefractive donor/acceptor density, due to the presence of the photochromic grating
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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