EFFECTS OF CARRIER COOLING AND CARRIER HEATING IN SATURATION DYNAMICSAND PULSE-PROPAGATION THROUGH BULK SEMICONDUCTOR ABSORBERS

Numerical modeling has shown that carrier cooling and carrier heating strongly influence saturation dynamics and pulse shaping in bulk semic onductor absorbers. With no electric field in the absorbing region, ca rrier cooling leads to strong additional fast saturation of absorption . The saturation causes a substantial decrease in the saturation energ ies for subpicosecond pulses in comparison with picosecond pulses. Com parison of bulk and quantum-well absorbers shows that fast saturation can be stronger in a bulk absorber, so bulk saturable absorbers may be interesting for usage in mode-locked solid-state lasers. Applying a n onzero electric field to a built absorber leads to strong carrier heat ing, which in turn suppresses absorption saturation. In this case, tra nsition to absorption saturation involves new mechanisms such as scree ning of the electric held by photogenerated carriers, as well as carri er cooling due to carrier-phonon interaction and by generated cold car riers. Carrier heating by the electric field causes the saturation ene rgy of the absorber to increase with the applied electric field. The i ncreased saturation energy allows one to shorten high-energy picosecon d and subpicosecond pulses without increasing the length of the satura ble absorber, which could be useful for the generation of high energy pulses with mode-locked and Q-switched semiconductor lasers.