Sub-picosecond region two dimensional parallel information processing in photorefractive crystals

点击翻译按钮获取中文摘要

We planned and carried out the following experiments : the pico-and subpico-second light pulses which bear the spatio-temporal information are recorded in and read out from volume holograms into which the temporal evolution is mapped spatially. For this aim, we developed the method to read out recorded gratings inside the volume hologram directly by measuring the diffraction efficiency and phase of cw laser beam as a function of angle detuning from the Bragg condition. The grating envelope function is obtained by solving the coupled mode equations inside the volume hologram. Then we recorded the interference fringes between the signal and reference beams, from the 3.5-picosecond duration mode-locked frequency-doubled Nd : YAG laster, inside a photorefractive LiNbO_3 crystal and could read out the information successfully.We measure the photorefractive sensitivities and time constants of LiNbO_3 and BaTiO_3 crystal for ultrashort pulses. We found that their responses strongly depended on the peak intensity of pulse, but they were independent of the pulse width. Especially, the sensitivity of LiNbO_3 increases an order of magnitude for intense input beams of several tens MW/cm^2. It is due to the intensity dependence of the photovoltaic effect. We also investigated the photorefractive effect of semi-insulating semiconductor GaP,and we obtained the information about its electrical state structure.