Measurements of gas temperature in HBr chemical lasers by TDLAS technique

Based on the Doppler broadening principle of absorption spectrum, the gas temperature measurement experiments of the optical cavity and the diffuser section were carried out on the D2/NF3 combustion-driven HBr chemical laser using the tunable diode laser absorption spectroscopy (TDLAS) technique. In order to effectively measure the TDLAS absorption spectrum, the R2 line of the HF molecular (2-0) vibrational band with a large absorption coefficient in the main gas flow was selected. In the experiment, a distributed feedback (DFB) diode laser with a center wavelength of 1 273 nm was used to build a HBr chemical laser gas temperature measurement system based on direct absorption TDLAS technique. By fitting the Voigt line shape to the absorption line of the HF molecule, the Doppler broadening width was obtained, and the gas temperatures of the optical cavity and the diffusing section were given. In the time domain frequency domain conversion, an F-P etalon with a free spectral range (FSR) of 1.5 GHz was used for frequency calibration. Experimental measurement results show that the temperature of the optical cavity is about 280 K and the temperature of the diffusing section is about 400 K. The ratio of collision broadening and Doppler broadening during the experiment is less than 0.1, indicating that the Doppler broadening is dominant, and the gas temperature of the optical cavity and the diffusing section can be conveniently monitored by the broadening of the HF absorption spectrum.