Saturation of band-gap resonant optical phase conjugation in HgCdTe

The saturation behavior of band-gap resonant optical nonlinearity is studied by degenerate four-wave mixing experiments at 10.6 microm in HgCdTe over a wide range of laser intensities. The reflectivity clips at a constant level when the laser intensity is increased above 100 W/cm(2), and the corresponding effective third-order nonlinear susceptibility drops as the inverse of the laser intensity. A theory based on the saturation of the interband absorption at the pump frequency resulting from state blocking is presented and agrees well with the experiment.