Kinetics of bleaching and induced absorption in glasses with CuInS2xSe2 (1–x) microcrystallites under picosecond excitation

We investigate the intensity dependence of the transmission and kinetics of the change in absorption of glasses with CuInS_2xSe_2(1–x) microcrystallites excited by 15 ps pulses at wavelengths of 1.08 and 0.54 μm. For photon energies slightly larger than the band gap, low excitation intensities (50 MW/cm²) lead to a bleached state with a relaxation time of ~11 ps. This effect is caused by a filling of quantum-well levels in the CuInS_2xSe_2(1–x) microcrystallites. As the pumping level increases, a fast (~40 ps) transition is observed from bleaching to strong induced absorption. The latter has a relaxation time of ~4 ns and is associated with two-photon interband transitions. At high pump intensities (≈ 10 GW/cm²), only induced absorption is observed. For photon excitation energies that considerably exceed the band gap, bleaching is not observed, and increasing the pump level leads to only an induced absorption. We have estimated the two-photon absorption parameter of glasses with CuInS_2xSe_2(1–x) microcrystallites at a wavelength of 1.08 μm. By using these glasses for mode locking of pulsed Nd:YAG and Nd:YAlO₃ lasers we have obtained ultrashort pulses with durations of 36 and 16 ps, respectively.