Recently, researchers from Shanghai institute of optics and Fine Mechanics (SIOM), Chinese Academy of Sciences (CAS) achieved the largest reported amount of pulse energy in a long-wave infrared laser at a kilohertz repetition-frequency band. A series of papers are published in IEEE Photonics Journal on May 6, 2021.
Firstly, the research group compresses the pulse width of the oscillator by designing the structure of the oscillator. Then, the average power of the seed laser is amplified by using a Ho:YAG amplifier. Lastly, by employing a ZGP OPO, the research group achieve the long-wave infrared laser with a pulse width of ＜10 ns and pulse energy of 3.15 mJ. In recent years, 8-12 μm long-wave infrared laser has been widely applied in many important fields, and high-average-power and narrow-pulse-width large-energy are gradually becoming the focus of attention. Therefore, the research team based on the technical route of 2.1μm Ho:YAG MOPA system pumping ZGP OPO, explored the limit pulse width of 2.1 μm Ho:YAG oscillator output laser.
After power amplification by a three-stage Ho:YAG amplifier, the research team use the 2.1 μm laser to pump ZGP OPO, and the experimental setup of the device is shown in Fig. 1.
The experimental results show that the pulse width of the Ho:YAG oscillator does not decrease when the repetition frequency is below 3 kHz, and stabilizes at ~12 ns, as shown in Fig. 2 and Fig. 3.
The power of the 2.1μm laser at 1 kHz and 3 kHz are amplified to 52.4 W and 72.1W, respectively. And the pulses are broadened to ~14 ns and ~17 ns after the three-stage amplification system. Based on ZGP OPO, 3.15W and 5.45W long-wave infrared laser outputs at 1 kHz and 3 kHz are achieved, corresponding to the pulse widths of 8.10ns and 9.45ns, respectively.
This scheme reveals the limit pulse width of long wave infrared laser achieved by ZGP OPO pumped by Ho:YAG MOPA system, and provides a method to obtain ~10 ns narrow-pulse and larger-energy long wave infrared laser.
The research was supported by the National Natural Science Foundation of China and related pre-research projects.

Fig. 1. Schematic diagram of experimental setup. (Image by SIOM)

Fig. 2. Output power of Ho:YAG oscillator. (Image by SIOM)

Fig. 3. Pulse width of Ho:YAG oscillator. (Image by SIOM)