Parametric study of photorefractive beam coupling in BaTiO3 at multiple wavelengths

Photorefractive behavior of batio3 crystals and their application in optical metrology in real time

Abstract: In this research we measure some of the optical parameters of Barium Titanate crystal (BaTiO3), such as signal beam gain, coupling constant (exponential gain coefficient), change in index refraction and photorefractive sensitivity, which are very significant for optical data storage. In all experiment, twowave mixing configuration at 632.8 nm (HeNe laser) were used. Experimental data for change in signal beam gain versus input angle of two beam, beam intensity ratio, pump beam intensity and grating vector, were plotted and compared with Kukhtarev theory. Using of experimental data, we calculated other optical parameters such as exponential gain coefficient, change in index refraction and photorefractive sensitivity. The results are good and the crystal can be used for optical data storage, dynamic holography, etc. For a wave mixing configuration,the same crystal as a recording medium for real time displacement has been used. For measurement of distant object a high coherent source such as HeNe laser has can been used. Long coherence length of the laser permit to study the objects which are far away from the crystal. The influence of intervening medium must be negligible.

Speckle shear photography using photorefractive crystals for in-plane strain measurement

Abstract: This paper present new optical configurations in speckle shear photography to measure in-plan displacement and the strain in real time using photorefractive (PR) crystals as recording medium. Speckle photography studies are made using a simple two-beam coupling configuration PR beam coupling in barium titanate crystals is characterized experimentally by measuring the signal beam gain and the exponential gain coefficient at 440 nm, 632.8 nm and 780 nm. In speckle shear photography, a diffused object illuminated with two parallel narrow laser beams is imaged inside the crystal, and a pump beam is added at this plane. The speckle patterns due to each beam and the pump beam produce index gratings. When the object is deformed, the speckle patterns shift consequently. We now have four speckle fields two generated from the interaction of pump beam with the index gratings and two pertaining to deformed states directly transmitted through the crystal. Thus, the fields from respective points on the object interfere after passage through the crystal and produce the Young's fringe patterns. Due to strain, the fringes in each pattern are of different width and orientation, resulting in the generation of a moire pattern. The strain is obtained from the width and orientation of the fringes in the moire pattern. The experiments are conducted on a specimen with a notch, which is subjected to tensile loading. The above studies are carried out at three different laser wavelengths, namely, 441.6 nm, 632.8 nm and 780 nm and the results are compared.

Figure-of-merit parameter of photorefractive crystals

Abstract: A comparative study of the photorefractive response of some commonly used ferroelectric, nonferroelectric and semiconducting crystals is presented. The figure-of-merit parameters such as steady-state change in refractive index, response time and photorefractive sensitivity tare evaluated for crystals of BaTiO 3 , LiBnO 3 , BSO, GaAs and InP on the basis of Kukhtarev's theory, using input parameters form reported data. These parameters are calculated as a function of the grating period with and without an application of 10kV/cm electric field. The results indicate that the choice of the ideal material for a given application can be made only after a careful comparison of the figure-of-merit parameters as trade-offs exist among the various parameters for any material.

Phase conjugation by diffraction gratings in photorefractive crystals

Abstract: Here we present four wave mixing configuration as one of the most important methods of generation and explanation of process of generation phase conjugation light the coupled equation was solved by three methods: undepleted pump approximation exact solution and two wave mixing approximation Although exact solutions can be derived for four-wave mixing, the results are difficult to use because of the complicated transcendental equation involved Solved the coupled equations and introduce an approximation in which two-wave mixing is the dominant process

Holographic storage in electrooptic crystals. i. steady state

Abstract: The non-linear theory of the self-diffraction on the light induced grating of refractive index in electrooptic crystals is developed. The intensities of the diffracted beams, the diffraction efficiency, and the shape of the surfaces of equal index change are calculated analytically for saturation holograms.Holographic storage in nominally pure reduced crystals of LiNbO3 is studied experimentally. It is shown that the developed theory in diffusion approximation satisfactorily describes the experimental data.

Adaptive optical networks using photorefractive crystals.

Abstract: The capabilities of photorefractive crystals as media for holographic interconnections in neural networks are examined. Limitations on the density of interconnections and the number of holographic associations which can be stored in photorefractive crystals are derived. Optical architectures for implementing various neural schemes are described. Experimental results are presented for one of these architectures.

Optical data storage by using orthogonal wavelength-multiplexed volume holograms

Abstract: We propose a volume holographic data storage scheme that employs counterpropagating reference and image beams and wavelength multiplexing for page differentation. This method is compared with that based on angular multiplexing. A reduction in holographic cross talk is predicted. Further cross-talk reduction that is due to sidelobe suppression is observed in experiments by using photorefractive crystals and the proposed orthogonal data storage.

holographic storage in electrooptic crystals. II. beam coupling—light amplification

Abstract: The theory of energy transfer between two coupled beams writing holograms in electrooptic crystals is developed. The gain is calculated for different processes causing holographic recording in the crystal.The amplifications of the light beam in the course of recording holograms in nominally pure reduced LiNbO3 crystals is investigated. The amplification of about 10 cm''-1 is obtained for small signals. The gain is found to be independent of the total light intensity and intensity ratio of the writing beams and decreases linearly with the grating spacing.

Coherent signal beam amplification in two-wave mixing experiments with photorefractive Bi12SiO20 crystals

Abstract: The amplification of the input signal beam in two-wave mixing experiments with photorefractive Bi 12 SiO 20 crystals is achieved when an additional phase shift is established between the photoinduced index modulation (phase volume hologram) and the incident fringe pattern. This stationary phase shift is introduced by either moving the crystal or the interference fringes at a constant speed. The transferred intensity is measured versus the applied electric field, fringe spacing and crystal velocity. The crystallographic orientation and the relative displacement with respect to the applied electric field polarity determine the amplitude of the energy transfer. For the first time in this crystal, signal beam amplification is reached for an applied field E 0 > 8 kV cm −1 and a crystal or fringe displacement speed around 5 μm s −1 at the green line ( λ = 514 nm ) of an argon laser.