为了获得高光束质量中红外激光抽运源，采用正分支共焦非稳腔设计Nd∶YAG脉冲固体激光器。在考虑晶体热效应情况下，对其腔型参量进行了数值模拟和试验验证，获得重复频率10Hz、脉冲宽度9.7ns、单脉冲能量260mJ、光束参量积3.5mm·mrad的激光输出。该激光经放大后抽运MgO∶LiNbO3晶体，实现波长3.85μm、脉冲宽度8ns、单脉冲能量104mJ的激光输出，光光转换效率为12.5%。结果表明，该抽运源光束质量满足高峰值功率中红外光参变振荡激光器使用要求，为光电对抗领域的应用奠定了技术基础。

To obtain high beam quality pump sources for mid-infrared lasers, a Nd∶YAG pulsed solid-state laser was designed with positive branch confocal unstable resonator. Under the influence of thermal effect, parameters of the positive branch confocal unstable resonator were optimized after numerical simulation and experimental verification. Single pulse energy of 260mJ, pulse width of 9.7ns and beam parameter product of 3.5mm·mrad were achieved at 10Hz. After amplification and pumping MgO∶LiNbO3 crystal, single pulse energy of 104mJ at 3.85μm was obtained with pulse width of 8ns, and its optical-optical conversion efficiency gets up to 12.5%. The results demonstrate that beam quality of laser pump source meets the requirements of the mid-infrared optical parametric oscillation laser. The research lays the technical foundation for its application in the field of optoelectronic countermeasures.