Abstract

The investigation of quantum coherence excited by femtosecond laser pulses is one of the central topics in quantum optoelectronics. Up to now, most investigations in semiconductors and semiconductor quantum structures deal with quantum coherence of excitonic states. For two reasons the quantum coherence of continuum states has not been anticipated for a long time due to i) the expected high momentum scattering rates of continuum states and ii) the dispersion of the valence and conduction bands, which gives rise to a strong "inhomogeneous" broadening of the band-to-band transitions. Recently, optically excited quantum coherence has been observed, which was attributed to the phase coherence of continuum states in the conduction band. These observations include Bloch oscillations in superlattices [1,2] and free-electrons in Landau levels [3]. Most recently, quantum coherence in the valence band has been observed in GaAs quantum wells [4] and bulk GaAs [5]. Here, we report on the observation of quantum coherence of the first heavy and light hole subbands in a GaAs quantum well under excitation above the fundamental excitonic transitions [4].

© 1997 Optical Society of America