High stability and low timing jitter passively Q-switched microchip lasers pumped with high repetition-rate square pulses

High peak-power laser pulses generated in the passively Q-switched (PQS) solid-state lasers have been widely used in material processing, optical communication, imaging, and ranging. PQS microchip lasers are well developed for generating high peak-power, nanosecond or sub-nanosecond pulses, however, it is a big challenge for achieving stable laser pulses in the PQS microchip lasers. Here, PQS microchip lasers are fabricated using Nd:YAG and Cr 4+ :YAG crystals as core components. Specifically, two Nd:YAG crystals with thicknesses of 1 mm and 2 mm serve as gain media, while three Cr 4+ :YAG crystals with distinct thicknesses and initial transmittances function as saturable absorbers. Under high-repetition-rate pulsed laser excitation, the PQS microchip lasers reliably produce highly stable Q-switched laser pulses. The generated laser pulses exhibit amplitude fluctuation and timing jitter of less than 1.5% and 0.7%, respectively. Stable single pulses with 10 μJ energy, 1.6 ns width, and 6.25 kW peak power are achieved in the PQS microchip laser pumped by 10 kHz repetition-rate pulses with 40 μs duration. When pumped by 20 kHz, 20 μs pulses, the PQS microchip laser generates stable dual pulses: the main pulse delivers 9.15 μJ energy, 2.3 ns width, and 4 kW peak power, while the satellite pulse features 2.5 ns width and 1.7 kW peak power. The 1064 nm laser pulses are further converted to stable 532 nm pulses via second-harmonic generation, and synchronization between the two wavelengths is realized, enabling potential applications in dual-wavelength high-resolution imaging.