Ultrafast hot-carrier dynamics in semiconductor saturable absorber mirrors

Femtosecond pump-probe experiments have been used to study the ultrafast nonlinear dynamics of InGaAs/InP semiconductor saturable absorber mirrors. The relative contributions of absorption bleaching and induced absorption are investigated by varying the excitation fluence over more than four orders of magnitude, well beyond complete absorption saturation. Enhanced free carrier absorption due to highly excited carriers with an extended relaxation time of 2.8 ps dominates the differential reflectivity at ultrahigh fluences and has been studied via a two-color pump-probe measurement.