Abstract

Using femtosecond pump–probe spectroscopy we have measured the development and subsequent decay of the gain and the recovery of the absorption. These optical nonlinearities are discussed in terms of phase-space filling, screening, and thermalization of carriers. Our calculations of the gain spectra for bulk GaAs are similar to the experimental gain data for GaAs quantum wells, indicating that quantum-confinement effects do not significantly influence gain dynamics. In narrow quantum wells we also observe a subpicosecond decay of the gain. This ultrafast (<400-fs) gain decay is explained in terms of plasma expansion.

© 1991 Optical Society of America