The nonlinear reflectivity of semiconductor saturable absorber mirrors is investigated with ultrafast time-resolved and time-averaged reflectivity measurements. The relative contributions of absorption bleaching and induced absorption are studied as a function of fluence and wavelength. The impact of induced absorption on the stability of continuous-wave mode-locking is considered theoretically. Picosecond pulses are produced from an Er/Yb waveguide laser using a semiconductor saturable absorber mirror, and the influence of two-photon absorption on mode-locking is studied. A semiconductor mirror exhibiting only induced absorption is used to stabilize a GHz repetition rate active harmonically mode-locked fiber laser, improving supermode suppression by eliminating pulse dropouts.
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