Coherent Pulse Breakup in Femtosecond Pulse Propagation in Semiconductors

Coherent pulse breakup is observed for below‐exciton resonance femtosecond excitation in a room‐temperature GaAs/AlGaAs multiple quantum well waveguide using the cross‐correlation technique. This pulse breakup is present only for large area pulses with durations less than the dephasing time of the closest exciton. For pulses longer than the exciton dephasing times, but with the same and even larger areas, the pulse breakup is not observed. The breakup is due to neither self‐induced transparency nor temperoral soliton. Instead, calculations based on the coupled semiconductor Maxwell‐Bloch equations show that coherent self‐phase modulation during propragation drives the system out of the initial adiabatic following regime into oscillatory excitation density, and eventually, pulse shape modulations.