Dual-comb spectroscopy for in-situ temperature measurements of gas-filled hollow-core fibers.

We demonstrate dual-comb spectroscopy (DCS) as an accurate and precise, non-contact, in-situ thermometry technique for gas-filled hollow-core fibers (HCFs). Measurements of the ν1+ν3 band of 12C2H2 are performed over a ∼4 THz bandwidth, and rotational temperatures and total column densities are extracted via Boltzmann analysis of Voigt-fitted transitions. Retrieved temperatures agree with independent platinum resistance thermometer measurements within the uncertainty derived from a combination of fit standard errors. Our results show temperature retrievals accurate to within 3% over a temperature range of 21-51 ∘C with a measurement precision better than 10% across 58 measurements. These results establish DCS as a powerful diagnostic tool for in-situ monitoring of HCF system performance.