SELF-EXCITATION OF SPACE-CHARGE WAVES

We report a direct observation of space charge waves in photorefractiv e crystals with point group 23 (sillenites) based on their penetration into an area with uniform light illumination. It is shown experimenta lly that the quality factor of the waves increases substantially with respect to what current theory predicts [B. Sturman el al., Appl. Phys . A 55, 235 (1992)]. This results in the appearance of strong spontane ous beams caused by space charge wave self-excitation.