  Results of experimental pump-probe spectroscopy of a quantum dash optical
amplifier biased at transparency are presented. Using strong pump pulses we
observe a competition between free carrier absorption and two-photon induced
stimulated emission that can have drastic effects on the transmission dynamics.
Thus, both enhancement as well as suppression of the transmission can be
observed even when the amplifier is biased at transparency. A simple
theoretical model taking into account two-photon absorption and free carrier
absorption is presented that shows good agreement with the measurements.
