Carrier dephasing in the gain region of an inverted semiconductor

The polarization dephasing time has been measured across the gain region, at the transparency point, and into the absorption region of an optically excited GaAs multiple-quantum-well sample using spectral hole burning and degenerate four-wave mixing techniques. We observe strongly energy-dependent dephasing rates with a minimum at the crossover from gain to absorption. Numerical results for the microscopically calculated carrier-carrier scattering rates for a two-component electron-hole plasma in quantum wells show fair agreement with the experimental findings.