Using a new optical configuration free from the influence of photorefractive optical nonlinearity, we investigate the main characteristics of the spatial subharmonic <i>K</i>/2 excited in a Bi<sub>12</sub>SiO<sub>20</sub> crystal by a light-intensity pattern with wave vector <i>K</i> and frequency Ω. It is shown that in a large region of intensity and applied electric field the optimum value Ω of the frequency corresponds to the conditions of parametric excitation of the weakly damped eigenmodes of the medium: the space-charge waves. The threshold and above-threshold characteristics of the subharmonic regime are in good agreement with the theory.
© 1995 Optical Society of America
B. I. Sturman, T. E. McClelland, D. J. Webb, E. Shamonina, and K. H. Ringhofer, "Investigation of photorefractive subharmonics in the absence of wave mixing," J. Opt. Soc. Am. B 12, 1621-1627 (1995)