PARAMETRIC OSCILLATION IN PHOTOREFRACTIVE MEDIA

We present an analysis of what is called parametric oscillation in pho torefractive media. It is shown theoretically that when a running grat ing and a constant electric field are applied to a photorefractive med ium it is possible for two secondary gratings to grow spontaneously. T hese theoretical predictions are subsequently verified experimentally in the crystal Bi12SiO20, and excellent qualitative agreement-is obtai ned. In previous subharmonic experiments, only grating vectors K/2, K/ 3, and K/4 were observed. Now, however, a whole continuum of grating v ectors has been observed. Thus subharmonic generation in photorefracti ve materials is simply a special case of parametric oscillation in whi ch the two secondary gratings are identical.