COHERENT PROPAGATION OF FEMTOSECOND OPTICAL PULSES IN A MONOCLINIC ZNP2 SINGLE-CRYSTAL

The free induction decay signal from excitons in a ZnP2 single crystal shows an unexpected temporal evolution, polariton beat, and coherent dip. We show that the effects come from a nonzero thickness of the sam ple and nonzero time width of the excitation pulses. A systematic nume rical calculation provides good qualitative agreement with the data. T hese effects are very important in understanding the experimental resu lts which deal with the coherent interaction between excitons and opti cal fields.