Detection of Bloch oscillations in a semiconductor superlattice by time-resolved terahertz spectroscopy and degenerate four-wave mixing.

We have studied the spatial dynamics of coherently excited wave packets of charge carriers in a semiconductor superlattice structure by both time-resolved THz spectroscopy and degenerate four-wave mixing. In the Wannier-Stark bias regime, we observe electron Bloch oscillations with a frequency that depends linearly on the electric bias field and can be tuned between a few hundred GHz and 5 THz.