Amplification, absorption, and lossless propagation of femtosecond pulses in semiconductor amplifiers

Light propagation in semiconductor amplifiers is investigated numerically for femtosecond pulses whose frequency spectra are fully inside the gain region. Whereas amplification is observed for low-intensity pulses, lossless propagation and even pulse absorption are found for large input intensities. These novel features arise from the competition between amplifying and absorbing states in the semiconductor continuum.