Estimation of diffraction efficiency of holographic gratings in photorefractive BaTiO_3 and BaTiO_3:Ce at multiple wavelengths

摘要

This paper is on the study of diffraction efficiency of photorefractive gratings recorded in two-beam coupling configuration in crystals of BaTiO_3 and BaTiO_3:Ce at multiple wavelengths. We study the distortive effects in a thick PR hologram due to the angle between the two interfering beams, modulation and the orientation of the crystal and measure the diffraction efficiency as a function of spatial frequency, modulation and the angle between the c-axis and the grating vector. The behaviour of both the crystals is compared at 441.6 nm, 632.8 nm and 780 nm using He-Cd, He-Ne and semiconductor diode lasers respectively. Value of diffraction efficiency of the undoped crystal is higher at 441.6 nm compared to other wavelengths whereas it is higher at 632.8 nm for the doped crystal. The difference in the spectral variation of optical absorption of the two crystals is found to affect the diffraction efficiency considerably. Diffraction efficiency is also estimated using Kukhtarev's theory and the results are compared with the experimental data.