Passively Q-switched Nd:YAG/KTA laser at 561 nm

We demonstrate a compact diode-pumped passively Q-switched Nd:YAG laser operating at the wavelength of 1123 nm, and its frequency-doubling into 561 nm by using a KTA crystal. The laser makes use of a single emitter 2.5 W laser diode, and at 561 nm puts out a 12 kHz pulse train of 4 ns, 5μJ pulses with an average power of 55 mW. The high pulse energy of the 1123 nm laser allows us to study the saturation of 1123 nm absorption in the Cr4+Cr4+:YAG Q-switch crystal. The ratio of the ground-state and excited-state absorption cross-sections is found to be σGSA/σESA=5.5±0.9σGSA/σESA=5.5±0.9.