Reflectivity kinetics of saturable absorbers for laser mirrors

Abstract

The reflectivity kinetics of saturable absorbers based on semiconductor quantum wells was investigated with differential reflectivity accuracy by the pump–probe technique for energy fluxes (0.27–5.40) photons cm−2 using a femtosecond Yb3+ :KY(WO4)2 laser. Three kinds of saturable absorbers were investigated: absorbers based on multiple quantum wells with nano-structured barriers grown over a mirror; the same absorber grown over the substrate; absorbers on multiple quantum wells separated by thick barriers grown over the substrate. The substrate contribution gives a stationary background and a two-photon absorption peak for small probe delays, which complicates the kinetics of the samples grown over the substrate. For absorbers grown over the mirror two exponential decays with a short relaxation time –0.4 ps and with a long relaxation time ps were obtained. The last relaxation time is remarkably shorter than in quantum wells with thick barriers.