种子注入单频脉冲光参量振荡器(OPO)是实现差分吸收雷达激光发射源的重要技术手段，且其输出光谱纯度直接影响探测气体对激光能量的吸收，进而影响该雷达系统的测量精度。就种子注入单频脉冲激光器而言，光谱纯度表征在其输出光谱中，种子波长成分所占的比例可以综合反映脉冲激光的输出线宽和频率稳定性等光谱特性。针对种子注入单频1.57 μm 脉冲OPO，理论上分析了光谱纯度的影响因素，设计并搭建了一套基于长程气体吸收池的光谱纯度测量系统。实验结果表明，当种子注入功率为26 mW，OPO 输出单脉冲能量为1.1 mJ时，种子注入单频脉冲OPO 的光谱纯度达到99.9%。

Injection seeding single frequency pulsed optical parametric oscillator (OPO) is an important technique to realize differential absorption lidar, whose spectral purity effects the energy absorption of laser pulses travelling via atmosphere directly and influences the accuracy of lidar system. Spectral purity demonstrates the ratio of seed mode energy to the whole pulse energy, which presents a comprehensive projection of spectral performances such as linewidth and frequency stability. In connection with 1.57 μm injection seeding OPO, factors influencing spectral purity are analyzed theoretically. A measuring system based on long path absorption cell is designed and built up. Experimental results show that spectral purity of injection seeding OPO can achieve 99.9% when seed injection power is 26 mW and OPO output energy is around 1.1 mJ.