Saturation of 640-nm absorption in Cr⁴⁺: YAG for an InGaN laser diode pumped passively Q-switched Pr³⁺:YLF laser

We measure the absorption recovery time, the ground- and excited-state absorption cross sections of a Cr⁴⁺:YAG crystal at 640 nm for the first time. A pump-probe measurement reveals the existence of two recovery times of 26 ns and 5.6 μs. By a Z-scan experiment, the ground- and excited-state absorption cross sections are estimated to be 1.70-1.75×10^-17 and 0.95-1.00×10^-17cm², respectively. The adequacy of the proposed model and the accuracy of the estimated parameters of the saturable absorber are verified by reproducing the experimentally obtained performance of a passively Q-switched Pr³⁺:YLF laser with the Cr⁴⁺:YAG saturable absorber from rate equation analysis.