Precise Gas Temperature Measurement Using a Single Dual-Wavelength Mode-Locked Fiber Laser

A single dual-wavelength comb fiber laser was designed to emit simultaneously two asynchronous ultrashort pulse sequences for gas temperature detection. The interpulse coherence can be easily realized by sharing the same cavity and experiencing the same environment, and complicated feedback control is no longer required. The asynchronous pulses yield an optical sampling for interferogram in the time domain. A heatable cell filled with acetylene and nitrogen was used as the target object. The absorption spectrum of acetylene from 6492.52 to 6496.4 cm-1 was obtained by performing fast Fourier transform (FFT) on the phase-corrected interferograms. The standard deviation (STD) of the residual error between the measured spectra and HITRAN database was within 0.01. A baseline-immune multispectral fitting method for gas absorption estimation was proposed to enable precise temperature calculation. Simulation results demonstrate that compared with two classical methods, i.e., the frequency-domain (FD) multispectral fitting method and time-domain (TD) molecular free-induction decay (mFID) method, the proposed method shows a higher accuracy of gas temperature and concentration measurement and is applicable to various baseline types and noises. In the experiment, compared with the two classical methods, the maximum relative error between the measured and reference temperatures of the proposed method was reduced to 3.2%. Simulation and experiment results verify that the proposed method yields higher accuracy and noise immunity than the two classical methods.