Absolute temperature measurements by direct-frequency-comb spectroscopy

The absolute temperature of acetylene gas is measured by an effective yet simple implementation of Doppler-broadening thermometry. At room temperature the combined measurement uncertainty is similar to 200 mK over 15 s measurement time. A large set of 28 lines in the near infrared region from 1.537 to 1.540 mu m, belonging to the P branch of the v(1) + v(3) rovibrational band of (C2H2)-C-12 and (CCH2)-C-13-C-12 at low pressure, has been addressed using for the first time a direct frequency-comb spectroscopic approach to retrieve the Doppler linewidths and hence the thermodynamic gas temperature. Experimental strate-gies to reach the millikelvin accuracy level are discussed. (C) 2020 Elsevier Ltd. All rights reserved.