Nonlinear absorption of Cr4+:YAG studied with lasers of different pulsewidths

Abstract

A saturable absorber Cr4+:YAG, used for a passive Q switching of Nd:YAG laser was studied in order to understand the physical mechanism of nonlinear absorption (photobleaching). An optical bleaching experiment was carried out using the two pulsed lasers with duration of pico- and nanoseconds at 1.064 μm wavelength. Experimental results were compared with numerical analysis of theoretical rate equations with all relevant energy levels. The inclusion of intersystem crossing between singlet- and triplet-excited states with reasonable rate of transition kisc was necessary to explain the difference in the saturation behaviors for nanosecond and picosecond laser pulses.