Superradiant emission from Bloch oscillations in semiconductor superlattices

The superradiant character of submillimeter-wave emission from optically excited electronic Bloch oscillations in a GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As superlattice is investigated by time-resolved terahertz emission spectroscopy. The intensity of the radiation and its decay time are studied as a function of the density of excited charge carriers. From the measured emission efficiency, the spatial amplitude of the charge oscillations is estimated. © 1996 The American Physical Society.