Terahertz Bloch oscillations in semiconductor superlattices

The coherent excitation of excitonic wavepackets in AlGaAs/GaAs superlattices is investigated in a comparative study employing three different timeresolved optical techniques. The experimental results obtained in time-resolved four-wave mixing (FWM), THz emission spectroscopy and transmissive electro-optic sampling (TEOS) provide the final proof of the existence of Bloch oscillations in the THz range. Each of these measurements provides complementary information on these oscillations. As a result, Bloch oscillations appear as a special case of quantum interference involving the coherent superposition of Wannier-Stark states.