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Absorption of High Intensity Femtosecond Pulses in Semiconductor Amplifiers

A. Knorr, R. Binder, E. M. Wright, and S. W. Koch

For picosecond or longer pulses the gain saturation model provides an adequate physical basis for understanding pulse propagation in semiconductor amplifiers. In this model only amplification of the output pulse energy with respect to the input can occur because the gain is saturated and the carrier density approaches its value at transparency (at transparency the propagation is lossless). We have observed extreme departures from the gain saturation model predictions in numerical simulations of femtosecond pulse propagation in semiconductor amplifiers. In particular, we predict absorption of high intensity input pulses even though the input pulse spectrum is fully inside the gain region.