Gas Temperature Measurement by Aligning Absorption Spectroscopy of Dual- Phase -Unlocked Optical Combs

An accurate gas temperature measurement method with dual-phase-unlocked comb absorption spectroscopy was presented. First, the spectra of interferograms (IGMs) of the dual-optical combs were aligned by full-spectrum cross-correlation. The frequency jittering of the spectra relative to the reference spectra was determined by cross-correlation and corrected by spectral shift. Second, a modified multispectral fitting approach was proposed to eliminate the wavelength-dependent intensity difference between the reference and measurement arms. The difference was eliminated to obtain the modified spectra by the differential operation without scaling between the two arms. Then, the gas temperature was calculated from the modified spectra. In the experiment, acetylene in a heatable airtight cell was employed as the target gas, and spectra over 0.8 THz were obtained. In the range from room temperature to 180 °C, the measured temperature agreed linearly with the reference, and the standard deviation of the temperature obtained by averaging 800 spectra for 1 s was less than 1.2 °C. The deviation between the mean value of measured temperatures and reference temperature did not exceed 1.9 °C.