High fluence ultrafast dynamics of semiconductor saturable absorber mirrors

The ultrafast nonlinear dynamics of InGaAs/InP semiconductor saturable absorber mirrors are investigated using reflective pump–probe measurements. At high fluence, ultrafast induced absorption begins to dominate over absorption bleaching. Above the InGaAs quantum well band gap, the differential reflectivity shows a ∼1 ps transient due to nonequilibrium carrier dynamics. Below band gap, the signal is dominated by a strong two-photon absorption component followed by induced absorption that decays with a time constant of ∼5 ps; these components are attributed to nonlinear absorption and subsequent carrier diffusion in the InP layer.