Adaptive running hologram recording and phase-shift measurement in photorefractive crystals

The author reports the use of phase modulation techniques in two-wave mixing (2WM) experiments for measuring the phase shift ψ between the interference pattern projected onto a photorefractive crystal and the resulting recorded hologram, as a function of the externally applied electric field E. Such data are used for computing the photoelectron trap density N_A in the crystal. Phase modulation techniques in conjunction with an adaptive fringe-locking method was also applied for running hologram recording under applied field E, which allows both matching of optimal recording conditions and measuring the `resonance´ hologram velocity v_o. From v_o vs. E data, the diffusion length L_D and the photoelectron generation rate g_o are found and the quantum efficiency for the process may be computed. Experimental results for Bi ₁₂SiO₂₀ (BSO) and Bi₁₂TiO₂₀ (BTO) are reported