Sbn Crystal Doped Photorefractive Wave Coupling Characteristics Of Study

Photorefractive crystals have many potential applications in optical image processing, optical data storage, optical interconnection, and optical computers. People developed many kinds of photorefractive nonlinear optical devices, such as volume holograph timing memorizers, optical image amplifiers and phase conjugation devices. Most of these applications have relations with beam-coupling in photorefractive crystals. The theories and experiments of the two-beam coupling in Cr-doped SBN:6 1 crystal is investigated detailedly in this thesis.Based on the band transport model, the formation of refractive index grating is discussed firstly. The steady solutions of two-beam coupling equations are deduced, and the conclusion is that the two-beam coupling process accompanies the energy transfer. From the absorption curves of various SBN crystals, we deduce that SBN:61 :Cr crystals should show great photorefractive properties by being irradiated with a He-Ne laser. We carry out two-beam coupling experiments in two SBN:61 :Cr crystals, and obtain the following results and phenomena: (1). There exists certain external beam crossing angle 20pcak at which the steady coupling coefficient F reaches the maximum. The values are approximately 200 and 27~ for l000ppm and 2000ppm SBN:Cr crystals, respectively. We point out that the existence of 20peak is the interactional result of the efficient electric-optic coefficient and the spatial electric field, and the range of the 2Opeak is calculated. (2). The steady coupling response time r is less than 0.8 sec, which is decreased as the increasing of 20, and a reasonable explanation is given out. (3). We also measured the relation of Fand the total beam intensity J~. (4). The different process of the energy transfer, the bistable state of the signal beam intensity and its different attenuation process are observed. The rational explanations are also presented. (5). The factors that can bring errors are briefly analyzed to minimize their influence. Three methods are provided to resolve the non-linearity of the optic-electric detectors, and the 損ost-disposal?method is applied to correct the experimental data. (6). The inside reflection of beams on the crystal?s surface is discussed. The conclusion is the inside reflection actually enhances the energy transfer through increasing the interactive length of the two beams. In the last part, some new applications are presented. The experiment results show that SBN:6l :Cr crystals have large coupling gains under the irradiation of He-Ne laser.