We previously concluded that RSA (reverse saturable absorption) is the key mechanism of optical limiting in CdSe/ZnS QDs by nanosecond pulses working simultaneously with “light quenching.” The limiting kinetics and OL mechanisms are significantly altered when the pulse duration is reduced [1,2,3]. In the event of ps-pulses and bright light, free carriers absorption became considerable. We show that the Auger relaxation through the 1S(e) states determines the limiting efficiency of laser light and absorption kinetics in CdSe/ZnS colloidal solutions for picosecond durations. In the measured kinetics of a probe-pulse transmission, a “delayed limitation” effect has been discovered. Using numerical modelling, the competition between the following two relaxation mechanisms of highly excited states has been identified: relaxing through size quantization levels and phononless relaxation through traps states.
Vladimir V. Danilov
Emperor Alexander I St. Petersburg State Transport University, Saint-Petersburg 190031, Russia.
Anastasia S. Kulagina
St. Petersburg Academic University, Saint-Petersburg 194021, Russia and ITMO University, Saint-Petersburg 197101, Russia.
Nickolay V. Sibirev
ITMO University, Saint-Petersburg 197101, Russia.