Influence of exciton-phonon scattering on self-induced transmission in semiconductors

Summary form only given. High-intensity pulse propagation of femtosecond laser pulses in optically thick semiconductor crystals can lead to self-induced transmission when the laser is tuned to a free exciton resonance. This effect means that at intensities on the order of MW/cm/sup 2/, pulses in the subpicosecond range lead to Rabi flopping of the carrier density. This causes the pulses to break up temporally after long-distance coherent propagation. The effect depends strongly on the coherence of the incident light field with the polarization of the exciton transition created in the semiconductor. Despite the expected excitation-induced dephasing, a large amount of coherent nonlinear transmission and a high contrast ratio of the Rabi flops are found at sample temperatures /spl les/10 K. In order to study the dynamics of the coherently driven polarization and the dependence on external dephasing, we introduced phonon-scattering by raising the temperature of our samples. The experiments were conducted with 800 fs pulses of an optical parametric amplifier in epitaxially grown CdSe. Our experiments clearly demonstrate that the coherent coupling of the free carrier polarization to the driving field of a high-intensity subpicosecond pulse with an area larger than /spl pi/ effectively prevents the expected dephasing by carrier-carrier scattering. Opening an additional dephasing channel by introducing phonon-scattering gradually weakens the coupling and suppresses characteristic features of self-induced transmission.