AN EXPERIMENTAL AND THEORETICAL-STUDY OF SPATIAL SUBHARMONICS IN A PHOTOREFRACTIVE BI12GEO20 CRYSTAL-INDUCED BY DC FIELD AND MOVING GRATINGTECHNIQUE

The generation of spatial K/2 subharmonics is reported for the first t ime to our knowledge in a photorefractive BGO crystal. The subharmonic instability regions in the applied dc field versus frequency detuning plane were measured for different interbeam angles and different modu lations of the interference pattern. The theory presented takes into a ccount both the modulation of the interference pattern and the presenc e of the fundamental space-charge field. There is good qualitative agr eement between theoretical prediction and experimental results.