体光折变栅的高阶衍射

本文探讨了在光折变晶体写入体相位栅产生高阶衍射的物理机制，在光栅的写入过程中，振幅和位相耦合分别引起光栅振幅和位相的不均匀，这两种不均匀性导致光栅波矢的附加横向分量，后者可有效地补偿高阶衍射的波矢失配，同时一旦高阶衍射在晶体表面出现，具有高增益值的光折变值晶体通过多波耦合将保证它随传播距离增长，这是在光折变晶体中形成高阶衍射光束的重要原因。

HIGHER ORDER DIFFRACTION OF VOLUME PHOTOREFRACTIVE GRATING

Physical mechanism of the origin of higher order diffraction beams of volume phase grating in photorefractive crystals is explored. During writing grating process amplitude and phase coupling cause strangely nonuniform in amplitude as well as in phase of the volume grating respectively.Both nonuniformities will result in the additional transverse component of the grating vector.The latter can compensate effectively for the wavevector mismatch of higher order diffraction.At the same time,once high.er order diffraction beams emerge on the crystal surface,the multiwave coupling in photorefractive crystals with high gain values will ensure its increase along with the increment of propagating distance.This is a dominant cause for formation of higher order diffraction.