LARGE PHOTOREFRACTIVE COUPLING COEFFICIENT IN A THIN CERIUM-DOPED STRONTIUM BARIUM NIOBATE CRYSTAL

Photorefractive two-beam-coupling coefficients are measured and compared in thin and thick cerium-doped strontium barium niobate crystals fabricated from the same boule. For extraordinary polarization, the thin sample exhibits an intensity coupling coefficient as high as 45 cm-1, whereas the highest coefficient measured in the thick sample is only approximately 14 cm-1. The measured dependences of two-beam coupling on beam-crossing angle, pump-probe beam ratio, and wavelength are compared in these thin and thick crystals; also, comparisons are made in photorefractive response times and optical absorption. We infer that the measured coupling coefficients in the thin sample are more reliable, and we attribute the reduced coupling coefficients in the thick sample to beam fanning. Beam fanning is incorporated into a coupled-wave theory to predict the reduced coupling coefficients in the thick sample, along with the dependence of the coupling on the pump-probe beam ratio.