Internal field dynamics of cohorent Bloch oscillations in supperlattices

The dynamics of coherent wavepacket oscillations in GaAs/AlxGa1-xAs superlattices are investigated by transmittive electro-optic sampling (TEOS) with femtosecond time resolution. The internal polarization dynamics of coherrently superposed Wannier-Stark states in an externally biased superlattice, denoted as Bloch oscillations, can be monitored with high sensitivity in TEOS experiments. The amplitude, dephasing, and frequency of Bloch oscillations are studied as a function of applied electric field. The increasing localization of Wannier-Stark states at higher fields results in a decreasing Bloch oscillation amplitude.