Multiwave mixing and soliton-like spatial structures in photorefractive crystals

Abstract

A theoretical model has been developed for multiwave mixing in media with photorefractive nonlinearity, making it possible to describe the process of interaction between the waves in the conditions exhibiting nonlinearities of different orders with due regard for the mixing geometry. Theoretically, the process of N -wave mixing at the N - 1 th -order nonlinearity has been described with the help of a band model for the photorefractive nonlinearity mechanism that includes the transitions from impurity levels within the band gap and enables description of the diffusion or drift processes in the external electric field. The energy efficiency of multiwave mixing and geometric parameters of spatial solitons in photorefractive Bi 12 TiO 20 crystals in the conditions of pulsed and continuous laser excitation have been studied experimentally. It has been found that switching-on of the photorefractive nonlinearity mechanism with 532 nmwavelength laser pulses requires a time interval in excess of 20 - 50 ns, with saturation beyond 80 ns. The formation dynamics of spatial solitons in photorefractive Bi 12 TiO 20 crystals has been analyzed with the use of continuous-wave radiation of a He-Ne laser. It has been determined that the formation conditions and dynamics are influenced by a number of factors including the geometry of radiation input into a crystal, power of the light beam, orientation of its polarization in the directions of the crystal axes, applied electric field and its direction.