Femtosecond pulse propagation in the gain region of laser amplifiers and applications to subpicosecond switching

Summary form only given. It has recently been predicted that femtosecond laser pulses with high enough intensity tuned inside the gain region should actually be absorbed rather than being amplified. This effect was explained as resulting from an interplay between the gain and absorbing regions. Pulses that are tuned inside the gain region interact resonantly with the gain states and nonresonantly with the absorbing states. These noninverted states behave like detuned absorbers in the temporal regions of adiabatic following. We have done experiments to investigate these effects. We tuned a self-modelocked Ti:sapphire laser operating at 90 MHz across the bandedge of a laser diode with 30 mA of injection current. The laser was tuned to the peak of the gain, and the transmission of the laser diode as a function of input pulse energy was measured. The laser diode initially exhibits gain saturation as the input pulse energy is increased, but rather than asymptotically approaching unity gain, the output pulse energy continues to decrease as the pulse undergoes induced absorption. We present our spectral hole burning measurements in the gain region.