OPTICAL INVESTIGATION OF BLOCH OSCILLATIONS IN A SEMICONDUCTOR SUPERLATTICE

We report the study of optical dephasing of Wannier-Stark ladder excitations in a semiconductor superlattice by means of transient degenerate four-wave mixing. We observe pronounced modulations of the signal with a time period varying linearly with the electric field. The time period,is found to equal the temporal periodicity of Bloch oscillations, in agreement with theory. In addition, we find that the dephasing time decreases with increasing localization of the Wannier-Stark states, which is attributed to carrier escape out of the lowest miniband.