Abstract

We have investigated the optical properties of GaAs quantum wells in the spectral region below the band edge using a two-wavelength picosecond optical pulse technique. Optical pumping in the transparent region produces modulation of the excitonic absorption which is probed with an optical pulse tuned to the excitonic absorption. We identify two distinct physical mechanisms that lead to the absorption modulation. First, a real population of carriers is produced by phonon-assisted absorption. These carriers bleach the excitonic transition by the action of the exclusion principle. The second mechanism involves virtual populations induced by the off-resonant optical excitation.

© 1987 Optical Society of America