Femtosecond dynamics in semiconductor lasers: Dark pulse formation

We track the dynamic response of GaAs quantum-well semiconductor diode lasers after injection of a femtosecond pulse, using ultrafast upconversion. The continuous-wave emission shows gain dynamics and relaxation oscillations on timescales of 1 to 100~ps. The recirculating femtosecond pulse evolves into an ultrafast 'dark pulse' in the wake of sub-picosecond oscillations