Coherent Inter-Valence Band Polarizations in Bulk GaAs Studied on a Sub-100 fs Time Scale

Coherent inter-valence band polarizations in the band-to-band continuum of GaAs are impulsively excited by 20 fs laser pulses. This leads to quantum beats with a frequency determined by the energy splitting between the optically coupled heavy and light hole states. The beat frequency is varied over a broad range between 5 and 30 THz by changing the spectral position of the laser pulses relative to the bandgap. The decay of quantum coherence occurs on a 150 fs time scale and is influenced by both inhomogeneous broadening and scattering processes.