Mid-bandgap electro-optic detection of Bloch oscillations

Summary form only given. Intense investigations of Bloch oscillations in semiconductor superlattices have been performed in four-wave mixing, THz emissions and resonant transmittive electro-optic sampling experiments. An intriguing objective of the studies is the experimental determination of the spatial amplitude of the oscillating electronic wavepackets in the artificial heterostructures. We present a novel technique for the determination of the amplitude of coherent Bloch oscillations in a semiconductor superlattice. In a two-color pump-probe setup Bloch oscillations are resonantly excited in a GaAs/AlGaAs superlattice (18 meV miniband width) by fs laser pulses derived from a Ti:sapphire oscillator. The longitudinal dipole field in the superlattice associated with the coherently oscillating electronic wavepackets relative to the localized holes is detected electro-optically in the center of the bandgap by a synchronously pumped optical parametric oscillator. The off-resonant detection based on the Pockels effect far away from optical transitions enables the quantitative determination of the coherent carrier motion with a time and space resolution below 150 femtoseconds and 1 nanometer, respectively.