Moving gratings and optical bias in holography with photorefractive crystal Bi12SiO20

Moving gratings at large fringe modulation and optical bias in photoreactive crystal Bi12SiO20 are investigated. With two-wave mixing architecture, the optimum fringe velocity and the enhancement of the diffraction efficiency exhibit strong nonlinear dependence on the fringe modulations. With four-wave mixing architecture, not only these nonlinear effects still exist but also the optimum pump beam ratio is totally different from a stationary grating. It is also found applying optical bias into moving gratings that the diffraction efficiency exhibits unexpected behaviour. Experimental results of these nonlinear effects are presented.