NONLINEAR FREE-INDUCTION DECAY IN SEMICONDUCTORS

An analytical investigation of nonlinear oscillatory free-induction decay (FID) has been carried out for narrow direct-gap semiconductors. The laser pulse duration t(P) is considered to be much smaller than the dephasing time of the semiconductor. The density matrix method is used to determine the response of the semiconductor by integrating over the \k> states involved in the coherent band-to-band transitions. In contrast to the oscillatory FID seen for atomic and molecular systems, the free-induction decay signal vanishes to zero very rapidly. However, for large pulse areas, at a time t(P) after the end of the pulse, there occurs a new phenomenon that can be termed "self-echo".