532nm测风激光雷达长时间稳频系统

Long-term frequency stabilization system in 532 nm wind lidar

中国科学院国家空间科学中心(空间中心)研制的532 nm多普勒激光雷达主要用于测量临近空间的大气风场、温度和密度等参数。获得单一的、稳定频率的出射激光是该多普勒激光雷达正常运转的关键技术。该激光雷达采用种子注入技术来获得单模的脉冲光,并通过将种子激光锁定在碘分子吸收线的方法来获得稳定的激光频率。调节种子光频率的方法有压电换能晶体(PZT)调节和温度调节两种机制。PZT调节的特点是调节速度快但调节范围窄,而温度调节的响应速度慢但调节范围大。通过协调两种调频机制,并利用比例-积分-微分(PID)控制算法,设计了一套长期稳定的锁频系统。该系统大大降低了对采集卡输出电压范围的要求,并可以使长时间的、大范围的频率漂移由调频较宽的温度调节来响应,而瞬时的频率漂移由响应速度较快的PZT调节来响应,从而保证了系统的长时间运行。该稳频系统的稳频精度可以达到350 k Hz。连续工作时长可达20 h以上。

The 532 nm Doppler lidar developed by the National Space Science Center, Chinese Academy of Sciences, is mainly used to measure the atmospheric wind field, temperature, and density. Maintaining a same reference frequency is a key technology to ensure the normal operation of the Doppler lidar. This lidar system uses seed injection technique to obtain a single mode pulse laser, and maintains the same reference frequency by locking the seed laser into the iodine absorption line. The frequency of the seed laser can be adjusted by two mechanisms： applying a voltage to a piezoelectric（PZT） crystal or changing the temperature of the laser crystal. The response speed of the two kinds of tuning mechanism is different. PZT tuning has a fast response speed but a narrow tuning range, while the thermal tuning has a wide tuning range and a low response speed. A long-term frequency stabilization system was designed by coordinating the two kinds of frequency tuning mechanism. And a Proportion Integration Differentiation（PID） algorithm was used to calculate the feedback voltage. The system did not require a acquisition card with a large range of output voltage. In this system, the laser frequency drift in long term and large range will be tuned by thermal tuning mechanism, while the instantaneous frequency drift will be responded by PZT tuning. The accuracy of the new frequency stabilization system is 350 k Hz. The system can work well as long as twenty hours.