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采用法布里-珀罗(F-P)标准具选模的脉冲单纵模激光器具有结构简单、紧凑、波长可调谐的特点,同时存在输出能量对腔长变化敏感、长期稳定性差的问题。针对此问题,本文根据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的主要因素,得到了频率、谐振腔长与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方法,设计了基于现场可编程门阵列(FPGA,Field Programmable Gate Array)的高速数字电路能量稳定系统。在控制过程中,对谐振腔长进行周期性调制,采用光电二极管(PD,photodiode)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,实现单纵模激光长期稳定输出。实验结果表明,采用此控制系统,纳秒脉冲单纵模激光器能量稳定性显著提高,连续工作3小时能量不稳定度(RMS)达到1.3%。
The pulsed single longitudinal mode laser modeled by the Fabry-Perot (F-P) etalon has the advantages of simple structure, compactness, and tunable wavelength. At the same time, the output energy is sensitive to cavity length variation and has poor long-term stability. In order to solve this problem, this paper analyzes the main factors that affect the output energy of this laser based on the working principle of single-mode laser generated by FP etalon, and obtains the relationship between frequency, resonant cavity length and laser energy. A dynamic feedback control Cavity length energy stabilization method, a high-speed digital circuit energy stabilization system based on Field Programmable Gate Array (FPGA) is designed. During the control process, the length of resonant cavity is periodically modulated, the intensity of nanosecond pulse laser signal is detected by photodiode (PD), and the longitudinal mode frequency caused by cavity length modulation directly affects the intensity of output laser signal. By analyzing Light intensity change information, calculate the length of the detuning cavity, as a basis for real-time cavity length compensation, thus forming a closed-loop control system to achieve long-term stable single-mode laser output. The experimental results show that with this control system, the energy stability of the nanosecond pulsed single longitudinal mode laser significantly increases, and the energy instability (RMS) reaches 1.3% after 3 hours of continuous operation.