We study coherent transient phenomena of excitons using femtosecond time-resolved four-wave-mixing (TR- FWM) in two types of high quality thin films of ZnSe; one is a homo-epitaxial film (1.2 μm thickness) and the other is a very thin (50nm) hetero-epitaxial film on GaAs substrate. Free induction decay (FID) behavior of the third-order polarization is clearly observed. We obtained the same values of exciton dephasing time from the temporal measurements, the decay time of FID, and the frequency domain measurements, analyses of reflection spectra. This implies that the excitons in ZnSe films are homogeneous. In the thin film sample, we observe a beat signal in time-integrated and time-resolved FWM. Based on the perturbational calculation, we conclude that the beat originates from the quantum interference of heavy- and light-hole excitons.
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