TECHNIQUES FOR THE ENHANCEMENT OF SPACE-CHARGE FIELDS IN PHOTOREFRACTIVE MATERIALS

Solutions to the band-transport equations are developed to include effects on the amplitude, dynamics, and spatialfrequency response of the space-charge field when periodic or dc electric fields are applied to a photorefractive material. Analysis of the effects of both idealized sinusoidal and square ac waveforms are given and compared with the case of resonant space-charge field enhancement with applied dc fields and moving fringes. Consideration is given to the effect of finite slew rate, uneven mark-space ratio, and other approximations to square ac waveforms. It is shown that the ideal square waveform provides the greatest enhancement of the space-charge field. It is also shown that in absorbing materials resonant enhancement with dc fields and moving fringes is localized to thin regions within the material, as the resonance condition is intensity dependent. This reduces the effective enhancement. Illustrative experimental results are presented for Bi12SiO20 and GaAs. © 1990 Optical Society of America.