Two-photon absorption in cadmium selenide

The nonlinear absorption coefficient β of a CdSe crystal was deduced from the attenuation of the radiation of a single-frequency neodymium laser at liquid-nitrogen and room temperatures. This was done for different orientations of the crystal. The coefficient β was several times higher than the values obtained for multimode laser radiation. Allowance was made for the space-time structure of the laser pulses and for the wave reflected from the exit face of the crystal. A study was made of the nonlinear absorption associated with the conversion of the fundamental-frequency radiation into the second harmonic whose frequency was located within the absorption band of cadmium selenide.