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/cm²) 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 LiNbO3is discussed.