Abstract

Femtosecond spectroscopy of semiconductors has identified a regime of coherent material response in which the polarization of the semiconductor and the electric field of the optical pulse couple in a phase-coherent way [1]. Most experiments have concentrated on excitonic polarizations with dephasing times in the picosecond regime, and phenomena like excitonic wave-packet propagation and/or quantum beats have been observed. In contrast, interband polarizations in the range of band-to-band continua show a photon-echo like time behavior with much faster dephasing [2]. In this paper, we report a new coherent phenomenon in the band-to-band continuum of a semiconductor. Quantum beats originating from the coherent nonlinear coupling of interband polarizations from the heavy (HH) and light hole (LH) band to the conduction band (CB) of GaAs are observed for the first time. The beat frequency is determined by the energy splitting of optically coupled heavy and light hole states and changes with the spectral position of the 20 fs laser pulses.

© 1996 Optical Society of America