Few-nanosecond gain-switched Ho:YAG and Ho:YAP lasers

Pulsed laser sources operating near 2 μm are essential for a wide variety of applications, including LiDAR, remote sensing, and medical applications, due to their eye-safety, high atmospheric transparency, and high absorption coefficient in tissue. While Q-switching is the common method to achieve laser nanosecond pulse durations, achieving sub-10 ns durations with high pulse energy remains challenging. The gain-switch method, though rarely implemented in the 2 μm spectral range, presents a compelling alternative due to its inherent simplicity and potential for producing short pulses in compact laser cavities. In this work, we demonstrate the performance of a very compact gain-switched Ho:YAG laser emitting at 2089 nm and report the first Ho:YAP gain-switched laser emitting at 2117 nm. Both lasers were pumped by a Tm:YLF laser operating at 1878 nm or at 1982 nm. The Ho-based crystals were selected due to their favorable emission cross-section and high LIDT. Besides the difference in emission wavelengths, the Ho:YAG is optically isotropic and does not have inherent birefringence, while the Ho:YAP is inherently birefringent, which enhances beam quality and polarization stability. Using direct gain-switching of the pump laser, pulses of 5 ns and energies up to 0.8 mJ at a repetition rate of 1.9 kHz were achieved using the Ho:YAG crystal. Pulses of 6.7 ns and energies up to 0.645 mJ at a repetition rate of 4.9 kHz were achieved using the Ho:YAP crystal. To the best of our knowledge, this is the first demonstration of gain-switching using both Tm:YLF and Ho:YAP crystals, yielding the highest reported peak power for a gain-switched Ho:YAP laser. These results highlight the Ho:YAP crystal as an efficient gain-switched laser at 2.1 μm, indicating significant potential for compact, high-energy, few-nanosecond pulsed laser sources in the SWIR region.