Timing jitter reduction of the sub-nanosecond Nd:YAG/Cr:YAG microchip laser via external optical triggering

A scheme to improve the temporal pulse stability of the passively Q-switched (PQS) sub-nanosecond Nd:YAG/Cr:YAG microchip laser was designed. By injection nanosecond laser pulses into the saturable absorber (SA) of the composite crystal, the SA is bleached compulsively to trigger the PQS laser and realize “optical synchronization”. As a result, the PQS sub-nanosecond laser pulses are locked to the injected pulses temporally and the timing jitter is greatly suppressed. In this work, the timing jitter of the PQS sub-nanosecond laser pulses was reduced from 561.2 ns to 344 ps using the nanosecond laser pulse as the reference signal, improved by over 1600 times, while the required pulse energy was merely at the level of 100 μJ. Based on the rate equations, a timing jitter model of the PQS laser was established by introducing random disturbance and injected photon number density, which could depict the temporal behavior and contributing factors. The dynamic process of locking the sub-nanosecond laser pulses was discussed by varying the injecting pulse energy, triggering time and peak pump power, with consistent theoretical and experimental results. It was also found that the pulse waveform, output power stability and beam quality benefit from optical triggering. This simple and efficient scheme of timing-jitter reduction lays the foundation for high-performance sub-nanosecond lasers, which is of great importance in high-precision ranging and lidar systems.