Room-temperature optical nonlinearities in bulk GaSe

Spectral dependence of the third-order optical nonlinearity in a bulk crystal of GaSe is studied at room temperature. The experimental techniques involved are nonlinear transmission and laser-induced self-diffraction. A theory of self-diffraction, which for the first time takes into account the multiple-beam interferences, is developed. The measurements are carried out, in the spectral range around the excitonic transition of GaSe. The refractive-index changes resulting from electron-hole plasma effect contribute to the generation of a phase grating below the band gap. (C) 1997 Optical Society of America.