NATURE OF NONLINEAR 4-WAVE-MIXING BEATS IN SEMICONDUCTORS

The nature of the beat modulations observed in nonlinear four-wave mix ing in semiconductors is determined by spectral resolution of the time -integrated four-wave-mixing signals. Beats between close-lying bound- exciton resonances in CdSe are found to be described by macroscopic po larization interferences between two noninteracting two-level systems. Beats between heavy-hole excitons and light-hole excitons in GaAs qua ntum wells, on the other hand, are described by a three-level system, i.e., as a true quantum interference phenomenon.