Generation of spatial subharmonics in a photorefractive semiconductor

Summary form only given. Subharmonics generation is a phenomenon originating from the excitation of so-called space charge waves (SCW) and instability of the photorefractive grating against these SCWs. It was found experimentally that spontaneous beams may occur when two plane waves with a small frequency detuning intersect inside the photorefractive Bi/sub 12/SiO/sub 20/ crystal in the presence of a DC electric field. These beams propagate in the directions corresponding to the diffraction from the gratings with grating vectors K/sub N/=K/N, K being the grating vector of the principal light-induced grating, with integer N, which is why the phenomenon was called spatial subharmonic generation. It was shown also that subharmonics may be generated with an AC electric field applied to the sample illuminated by a stationary interference pattern. While the theory predicts subharmonics excitation for photorefractive semiconductors, they were never observed before in crystals other than various sillenites. We report on first experimental observation of the spatial subharmonics in germanium doped cadmium telluride and show in that this phenomenon is quite general for photorefractive materials and is inherent not only to the sillenite-type crystals.