采用法布里-珀罗(F-P)标准具选模的脉冲单纵模激光器虽具有结构简单紧凑以及波长可调谐的特点, 但存在输出能量对腔长变化敏感、长期稳定性差等问题。针对这些问题并根据F-P标准具产生单纵模激光的工作原理, 分析了影响此类激光器输出能量稳定性的主要因素, 得到了频率、谐振腔长与输出激光能量之间的关系, 提出了动态反馈控制腔长的能量稳定控制方法, 设计了基于现场可编程门阵列的高速数字电路能量稳定系统。利用所提控制方法对谐振腔长进行周期性调制, 采用光电二极管探测纳秒脉冲激光信号的强度。腔长调制引起的纵模频率变化直接影响输出激光信号的强度, 通过分析激光强度变化的信息, 计算腔长失谐量, 以此为依据进行实时的腔长补偿, 从而形成闭环控制系统, 实现单纵模激光的长期稳定输出。实验结果表明, 采用所提控制系统时, 纳秒脉冲单纵模激光器能量稳定性得到显著提高, 连续工作3 h的能量不稳定度达到1.3%。

A pulsed single-longitude-mode laser which uses a Fabry-Perot (F-P) etalon to select mode has advantages of simple compact structure and tunable wavelength. However, the output energy of the laser is sensitive to the change of cavity length, and the long-term stability is poor. To solve these problem, the main factors affecting the stability of output energy are analyzed based on the principle of single-longitude-mode laser with F-P etalon. The relationship among frequency, resonant cavity length and energy of output laser is obtained. An energy stability control method of dynamic feedback control cavity length is proposed. A high-speed digital circuit energy stabilization system based on field programmable gate array (FPGA) is designed. The length of resonant cavity is controlled periodically with the proposed method, and the intensity of the nanosecond pulsed laser signal is detected by photodiode. The frequency variation of longitudinal caused by the cavity length modulation directly affects the intensity of the output laser signal. The information of laser intensity change is analyzed, and the cavity length detuning is calculated. Based on this, the cavity length compensation is realized and a closed-loop control system is formed. Finally, the long-term stable output of the single-longitude-mode laser is achieved. Experimental results show that energy stability of the nanosecond pulsed single-longitude-mode laser is significantly improved with the proposed control system. The energy instability of continuous working for 3 h is 1.3%.