Design of a laser temperature controller and its application in absorption spectral based gas sensing

A homemade temperature controller, which features with robust and inexpensive, is designed for actively adjust and stabilize the operating temperature of the tunable semiconductor diode laser. The accuracy of this temperature controller is +/- 0.05K, which corresponds to 0.035 cm-1 in wavenumber for our selected laser diode with a center wavenumber of 6045.949 cm-1. This temperature controller uses the STM32H743 (an ARM processor) as the control core, and introduces a capacitive touch screen to realize the visualization of experimental data and the intuitive of human-computer interaction. Through the simulation using software, the performance of conventional PID algorithm and adaptive fuzzy PID algorithm are compared and analyzed. Based on this, the fuzzy PID control strategy is determined and implemented through programming. In order to improve the efficiency and the stability of the ARM processor, the temperature control process is divided into several threads such as temperature acquisition, control quantity calculation, PWM output, temperature data/curve display, and SD card storage. The RTX5 operating system is ported to manage the cooperative operation of the above tasks and the communications between them. Using wavelength modulation spectroscopy, measurements of methane concentration are carried out in a laboratory controlled environment (P ∼ 1 atm, T ∼ 296 K) to validate the proposed temperature controller. In a stainless cell, the experiments are carried out using five samples with their concentrations ranging from 1000ppm to 2%, and a 5ppm detection limit is determined by nonlinear regression analysis, with a regression coefficient as high as 0.9979.