Free Carrier Induced Third Order Optical Nonlinearities in Semiconductors*

Abstract

We have studied a variety of free carrier induced optical nonlinearities in III-V and II-VI semiconductors and compounds by four-wave mixing experiments with Q-switched CO2 lasers. Third order susceptibilities χ(3) in excess of 10-3 esu with picosecond recovery times have been observed. Because of their rapid recovery, these nonlinear processes can operate at high laser intensities without saturating. The dispersion of the susceptibility provides a easy method to determine relaxation times in the 0.1 to 5 ps. range.