Development of a multi-pass cell temperature control system for laser gas isotope detection

The gas isotope abundance can be detected by laser absorption spectroscopy method. As the absorption coefficient of the absorption line of the gas to be measured can be affected by the temperature of the gas to be measured, the temperature of gas will directly affect the accuracy and stability of the gas isotope detection system. A high-precision multi-pass gas cell temperature control system was designed and developed in this paper. In hardware, a high-accuracy PT1000 platinum resistance temperature acquisition circuit and a polyimide electrothermal film heating device were used to form a complete closed-loop temperature control structure. In software, Ziegier-Nichols' engineering setting method was used to complete the three coefficient settings of P, I, and D. Aiming at the problem that a large amount of overshoot caused by the complex structure and slow response of the controlled object, the integral separation PID control algorithm was used to make the temperature control fast and without overshoot. The system was used for temperature control experiments, experimental results show that the temperature control range was 18-42℃, the temperature control precision is 0.08℃, and the stabilization time is 15 s. This multi-pass gas cell temperature control system has the advantages of high precision and fast response and no overshoot, which provides reliable guarantee for laser gas isotope detection.