Nanosecond green pulse trains generated in a burst-mode by a Cr:YAG Q-switched Nd:YAG laser

We present the development and characterization of a nanosecond-pulsed Nd:YAG laser operating in burst-mode and passively Q-switched using a Cr:YAG saturable absorber. The system is examined in three configurations: free-running, passively Q-switched, and frequency-doubled using an external KTP crystal. In free-running operation, the laser delivers 618 μs pulse duration with a peak output voltage of 12.47 mV. In the Q-switched regime, four cavity lengths are investigated, showing that shorter cavities significantly reduce the Q-switching threshold while increasing both the repetition rate and the number of pulses within each burst. The optimized 275-mm cavity produces bursts containing up to 22 pulses with 45 ns duration and a 56 mV peak voltage at an intra-burst repetition rate (frep) of 7.142 kHz repetition rate. Pulse energy is estimated from the linear voltage response of an InGaAs fast photodetector to incident optical power. The temporal spacing between consecutive bursts is 13.12 ms, and each burst lasts approximately 250 μs. By integrating an external KTP crystal, second-harmonic generation at 532 nm is achieved, producing 6 ns green pulses with a 65.2 mV peak voltage at an intra-burst repetition rate (frep) of 3.846 kHz. Beam instabilities related to SHG, known as the “green problem,” are also observed. These results provide useful guidelines for optimizing burst-mode Q-switched lasers for efficient nanosecond pulse generation and frequency-doubling applications.