Coherent wavepackets and phonons in superlattices

Coupled Bloch-phonon modes are investigated in GaAs-Al/sub 0.3/Ga/sub 0.7/As superlattices with electronic miniband widths larger than the GaAs LO phonon energy of 36 meV. Bloch oscillations are excited by a 50 fs laser pulse from a Ti:sapphire laser with the excitation energy tuned in resonance with the lower branches of the Wannier-Stark ladder. The dynamics of the coherent motion of the Bloch wavepackets is traced in time-resolved electrooptic transmission and reflectivity experiments.