High-repetition-rate 300-ps pulsed ultraviolet source with a passively Q-switched microchip laser and a multipass amplifier

We demonstrate a new kind of picosecond laser source in the UV at a high repetition rate of $-45 \mathrm{kHz}$, using only passive, compact, and simple elements. This system is based on a microchip laser and a very efficient multipass amplifier, both pumped with recently developed high-brightness laser diodes. The system has been optimized to deliver, at a high repetition rate, subnanosecond pulses at the wavelength 355 nm with an energy per pulse of close to $1 \mu \mathrm{J}$ (38-mW average power). This source is to our knowledge the first totally passive 300-ps UV laser source at this high repetition rate.