ULTRAFAST NONLINEAR OPTICS DUE TO ELECTRON-HOLE PLASMA IN BULK SEMICONDUCTORS

It is theoretically demonstrated that, in the presence of an electric potential landscape, the ground-state energy of the electron-hole plas ma can be substantially lowered against the ground-state energy of the excitons. The electron-hole plasma is found to be unstable at lower c arrier densities. The critical carrier density for the transition betw een these two states can be reduced. This reduction provides a new mec hanism of nonlinear optics for bulk direct band-gap semiconductors, wi th picosecond relaxation time, large nonlinearity, and requiring low p ump intensity.