KINETICS OF THE HIGHER-ORDER RESPONSE OF PHOTOREFRACTIVE MATERIALS

The analytic expressions for the first three higher-order harmonics of the space-charge field versus time are obtained by use of the hopping model of Feinberg et al. [J. Appl. Phys. 51, 1297 (1980)]. The result s are valid for arbitrary strengths of characteristic fields in the ph otorefractive materials with arbitrary values of the modulation depths . The dependence of the fundamental space-charge field on the higher-o rder fields is strong as the modulation depth increases. There is an a pparent peak that originates from the contributions of the higher-orde r harmonics during the evolution of the fundamental harmonic of the sp ace-charge field. We also determine the next-order correction to the f undamental space-charge field, which indicates that the ratio of the n ext-order correction term to the fundamental term is strongly dependen t on the modulation depths m. (C) 1996 Optical Society of America.