MOVING GRATING METHOD IN PHASE-CONJUGATION - PRINCIPLE, METHOD AND ITS APPLICATION

By means of the moving grating method, the phase shift between interfe rence pattern and refractive index grating formed in a photorefractive crystal can be freely controlled. For this purpose, we shifted the fr equency of an incident light by using the Doppler effect with a piezoe lectrically driven mirror. Reflectivities of the phase conjugation in Bi12SiO20 (BSO) and Bi12GeO20 (BGO) crystals were remarkably enhanced up to 490and to 430response time t. Dependences of t of BSO on applied electric field, grating period and incident light intensity were meas ured precisely. The result was found to agree satisfactorily with the theory based on the charge transport equations with already-known mate rial constants such as donor and trap densities, photoionization cross section, mobility, recombination constant. In the case of BGO, trap d ensity and a product of photoionization cross section and donor densit y which had not been known yet, were determined by the least-squares f itting with the result of the same experimental procedure as BSO.