Femtosecond absorption bleaching in glasses with semiconductor nanoparticles

摘要

Pump-probe femtosecond transmission measurements in the vicinity of the first excitonic resonance are performed in a silicate glass embedded with Cd-S-Se semiconductor nanoparticles. In the experiment, the pump at 400 nm (duration 50 fs, energy up to 0.1 mJ) excites the sample, while the change of the optical absorption is probed by femtosecond continuum. The time-resolved spectrum of the absorption change in the wavelength range 450-650 nm is visualized using a two-channel imaging spectrometer. A strong optical nonlinearity of the glass containing Cd-S-Se nanoparticles results in the up to 50% bleaching of the first excitonic resonance via the depopulating of the ground state. The temporal evolution of the bleaching consists of fast (with relaxation time as small as 3 ps) and slow (＞ 15 ps) components. The dependence of the nonlinear absorption on the detuning of the pump and probe wavelengths with respect to the exciton resonance is evaluated.