Short-pulse grating formation in photorefractive materials

Solutions are obtained for the refractive index grating in a photorefractive material in which the writing or erasing beams are short-pulse (less than tens of nanoseconds), high-irradiance (greater than kW/sq cm) lasers. The response of the photorefractive material is modeled using the continuity equation for the charge carriers, a rate equation for the ions, a current equation, and Poisson's equation for the space charge field. Two cases are discussed in detail: (1) the time for recombination of carriers with ions is much less than the pulse length of the laser; and (2) the recombination, drift, and diffusion times are all much longer than the pulse length. The energy requirements for short-pulse writing and erasing are greater than or equal to those obtained for typical CW lasers in all cases investigated. Application to previous observations in BaTiO3, Bi12SiO20, and LiNbO3 is discussed.