INVESTIGATION OF PHOTOREFRACTIVE SUBHARMONICS IN THE ABSENCE OF WAVE MIXING

Using a new optical configuration free from the influence of photorefr active optical nonlinearity, we investigate the main characteristics o f the spatial subharmonic K/2 excited in a Bi12SiO20 crystal by a ligh t-intensity pattern with wave Vector K and frequency Omega. It is show n that in a large region of intensity and applied electric field the o ptimum value Omega of the frequency corresponds to the conditions of p arametric excitation of the weakly damped eigenmodes of the medium: th e space-charge waves. The threshold and above-threshold characteristic s of the subharmonic regime are in good agreement with the theory.