Hyper-Raman Gain due to Excitons Coherently Driven with Femtosecond Pulses

Abstract
We report the observation of optical gain in the transparency region of gallium arsenide highly excited by femtosecond pulses just below the excitonic resonance. We find a very good agreement of the pump-probe spectra with a model based on the fifth-order development of the time-dependent density operator.