Ultrafast nonequilibrium carrier dynamics in semiconductor laser mode locking

Semiconductor disk lasers have been shown to be ideal as wavelength-agile, high-brightness sources for producing high average power under various pulsed mode-locking scenarios. Systematic microscopic modeling reveals that ultrafast nonequilibrium kinetic hole burning in electron/hole carrier distributions dictates the outcome of femtosecond duration mode-locked pulse formation. The existence of a large reservoir of unsaturated carriers within the inverted distributions leads to the emergence of multiple pulse waveforms (not necessarily harmonically mode-locked pulse trains) that inefficiently draw on these carrier reservoirs. The concept of gain is no longer meaningful in this limit, and the dynamical inversion of electrons and holes primarily in the active medium establishes the final dynamical state of the system. The simulation results explain much of the generic behavior observed in key recent experiments and point to the difficulty of pushing semiconductor mode-locked lasers to pulse durations below 100 fs.