大 尺 寸 磷 锗 锌 晶 体 生 长 及 其 在 中 波 红 外 激 光 输 出 方 面应 用 的 研 究 进 展（特 邀）

Significance Mid-wave infrared (MIR, 3 ‒ 5 μm) lasers with high power and large energy output have attracted significant attention due to their broad application potential in optoelectronic countermeasures, infrared medicine, and laser communication. As the key component of solid-state MIR laser systems, ZnGeP₂ (ZGP) crystals must be large and exhibit low absorption loss to enable efficient nonlinear frequency conversion, thereby achieving hundred-watt-level high power and hundred-millijoule-level large energy output. This review focuses on the development and application of large-size ZGP crystals for MIR laser generation. It systematically summarizes recent advances in ZGP crystal growth, high-power and high-energy MIR laser output, and the miniaturization of MIR lasers. The paper also highlights our group′s progress in growing large-size ZGP crystals and fabricating large-aperture optical devices. Finally, current technological challenges are analyzed and future research directions for advancing this field are proposed. Progress According to recent reports from leading domestic and international research institutions (Fig. 1, Fig. 2), the growth size of ZGP single crystals has generally surpassed the Φ50 mm scale. However, due to limitations in post-processing techniques and challenges in maintaining optical homogeneity, the practical device aperture is currently constrained to a maximum of approximately 25 mm×25 mm, with device lengths ranging from 30 to 50 mm (Fig. 8). The advancement of large-size crystal growth technology not only provides a critical foundation for fabricating large-aperture nonlinear optical devices but also enables multiple devices to be sliced from a single ingot, thereby significantly reducing unit production costs and enhancing overall manufacturing efficiency. Despite this progress, large-size ZGP crystals and devices continue to face technical challenges, including the control of compositional and optical uniformity, the suppression of structural defects, and the enhancement of laser-induced damage thresholds. To further improve crystal quality and device performance, ongoing research efforts are focused on optimizing growth parameters, employing elemental doping strategies, and developing advanced post-processing techniques. In the development of high-power MIR laser systems, ZGP-based optical parametric oscillators and amplifiers (OPO/OPA) have emerged as core technological approaches. When combined with Ho∶YAG lasers as efficient pump sources, this configuration has successfully achieved MIR laser outputs exceeding 100 W, thereby significantly advancing the upper power limits of MIR laser technology, as detailed in Table 2. To further enhance output power and optical-to-optical conversion efficiency, research has focused on the integration of multi-stage master oscillator power amplifier (MOPA) architectures, the use of low-absorption ZGP crystals, and the implementation of compact resonator cavity designs. These advancements aim to meet the growing demand for high-power, high-efficiency mid-wave infrared (MWIR) laser systems in critical application areas such as infrared countermeasures, remote sensing, and space-based optical communications. High-energy MIR lasers are primarily realized through OPO and OPA techniques, which utilize nonlinear frequency conversion in ZGP crystals pumped by high-energy 2.1 μm laser sources, as illustrated in Table 3. To enhance pump energy and beam quality while mitigating thermal effects within the nonlinear crystal, a high-energy Ho∶YAG MOPA system is employed, incorporating multi-stage amplification and precise spectral control. Through doping engineering and optimization of crystal growth parameters, the absorption coefficient of ZGP in the pump band is significantly reduced, effectively suppressing thermal lensing and increasing the energy handling capacity of the crystal. These advancements collectively support the development of joule-level, single-pulse MIR laser systems operating at repetition frequency exceeding 1 kHz—systems that are crucial for next-generation applications in directed-energy laser weapons, deep-space exploration, and other frontier scientific and defense technologies. Pulsed thulium (Tm)-doped lasers, commonly configured with linear resonant cavities, are widely used as direct pump sources for ZGP OPO. These systems offer key advantages, including compact size, ease of miniaturization, low lasing threshold, and high peak power density. With ongoing advancements in ZGP crystal growth and post-processing technologies, the absorption coefficient at 1.907 μm has been successfully reduced to below 0.05 cm^-1, enabling efficient pumping in the 1.9 μm band. This wavelength coincides with the gain peak of Tm-doped fiber lasers, which is particularly beneficial for suppressing nonlinear optical effects and reducing amplified spontaneous emission (ASE). Moreover, the reduced absorption at this pump wavelength mitigates thermal accumulation within the ZGP crystal, thereby improving both nonlinear frequency conversion efficiency and the output beam quality of mid-wave infrared lasers. Based on these considerations, future development of miniaturized ZGP-based MIR laser systems should focus on three key directions: increasing the power of pulsed Tm-doped fiber lasers, optimizing OPO cavity geometries, and further minimizing the near-infrared absorption of ZGP crystals. These efforts are expected to significantly enhance pump efficiency and support the advancement of high-performance, compact mid-infrared laser sources. Conclusions and Prospects All-solid-state lasers based on ZGP crystals for optical frequency conversion have emerged as a leading technology for generating MIR laser sources, owing to their advantages in compactness, lightweight design, high efficiency, high output power, and continuous wavelength tunability. Recent advancements in high-average-power, high-repetition-frequency Ho∶YAG lasers have driven considerable progress in ZGP OPO and OPA systems, enabling mid-infrared laser outputs exceeding 100 W and expanding their potential in applications such as infrared countermeasures, remote sensing, and space-based optical communications. Future research will focus on four key areas: (1) scaling power and energy through multi-stage amplification in Ho∶YAG MOPA-driven ZGP cascaded systems, which have already demonstrated >100 W and >100 mJ single-pulse output; (2) enhancing conversion efficiency beyond the current ~70% limit, which is constrained by phase-matching and pump characteristics, through the development of low-absorption ZGP crystals; (3) achieving miniaturization and integration by employing sub-2 μm pump sources, compact cavity architectures, and optical MOPA systems to reduce system size while maintaining performance; and (4) improving beam quality through image-rotating non-planar ring cavity OPOs, with further enhancements in tunability and power anticipated through advanced resonator designs or MOPA integration. In summary, while the performance of ZGP-based solid-state lasers is presently limited by the output characterization of pump source and the absorption and damage thresholds of ZGP crystals, future advancements in pump engineering and crystal optimization are expected to enable mid-infrared systems with hundreds of watts of output power, joule-level pulse energy, conversion efficiencies exceeding 70%, high beam quality, and compact form factors, thereby meeting the stringent requirements of next-generation optoelectronic applications.