500 Hz Joule-level output by sub-nanosecond Zig-Zag slab laser

  Objective  The high-energy, high-repetition-rate sub-nanosecond lasers have been widely applied in various fields such as industry, military, and scientific research due to their superior peak power compared to nanosecond lasers and enhanced stability compared to femtosecond lasers. Researchers have discovered that sub-nanosecond lasers have a lower threshold for causing complete damage to optoelectronic devices compared to nanosecond and femtosecond lasers. Therefore, high-repetition-rate, high-energy sub-nanosecond solid-state lasers offer significant advantages in the field of optoelectronic countermeasures. Currently, under conventional water cooling conditions, the single-pulse energy of high-repetition-rate lasers has surpassed the hundred-millijoule level. However, for optoelectronic countermeasure applications, higher repetition rates and higher single-pulse energies are required to improve the hit rate on rapidly moving targets. Thus, the breakthrough of higher repetition rates and high-energy sub-nanosecond lasers is urgently needed.

  Methods  This paper presents the realization of Joule-level sub-nanosecond laser output by combining end-pumped microchip crystal picosecond laser generation technology and multi-pass multi-stage slab laser amplification techniques. Initially, the microchip laser is pre-amplified through a three-stage end-pumping process, scaling the microjoule-level energy to millijoule-level. Subsequently, the shaped laser beam with a size of 2×18 mm² is injected into a first-stage single-end-pumped slab amplifier system. The amplified laser is then transmitted through a first-stage imaging and beam expanding system before being injected into a second-stage dual-end-pumped double-pass amplifier system. Finally, the laser is further amplified through a third-stage single-pass booster amplifier in the slab configuration. This study presents the design of a dual-end pumping structure (Fig.1), with the omission of the isolation system.

  Results and Discussions   In the dual-end-pumping structure, the energy of the leaked pump light can directly cause damage to the pumping module. In this study, experimental results revealed significant fluctuations in the energy of the leaked pump light with variations in the pump current and pump module cooling temperature (Fig.2(a)). Therefore, by controlling the cooling temperature of the pumping module, it is possible to regulate the energy of the leaked pump light at different pump currents, thereby avoiding damage to the pumping module and eliminating the need for complex isolation devices. Using the temperature-controlled dual-end pumping technique, the research team amplified the seed light from 3.12 mJ at 500 Hz to 952 mJ (Fig.2(b)) with pulse width of 680 ps, under the conditions of a first-stage and second-stage pump cooling temperature of 25 ℃, and a second-stage pump cooling temperature of 23 ℃. The amplification energy levels in Fig.2(b) were measured after the output of the third-stage slab amplifier. The sub-nanosecond laser output with Joule-level energy and a repetition rate in the hundreds of hertz achieved by this system represents the highest parameters currently achieved in the field of slab lasers.

  Conclusions  This paper reports a high-repetition-rate, high-energy Nd:YAG low-doped slab laser. The laser utilizes a high-power master oscillator power amplifier (MOPA) structure, with a single longitudinal mode microchip laser as the seed source, and achieves amplification through a three-stage slab system with beam shaping. The study demonstrates that the leaked pump light in the dual-end-pumped slab amplifier can damage the pumping module. However, precise control over the energy of the leaked pump light can be achieved by controlling the cooling temperature of the pumping module, effectively avoiding damage to the pumping module. In this work, using temperature-controlled dual-end pumping technique, we amplify the seed light from 3.12 mJ at 500 Hz to 952 mJ with a pulse width of 680 ps. This work provides an effective pump cooling solution for high-energy, short-pulse lasers, ensuring their stable operation, thereby paving the way for the application of high-repetition-rate, high-energy sub-nanosecond slab lasers in the field of optoelectronic countermeasures.