Leveraging resonant frequencies of an optical cavity for spectroscopic measurement of gas temperature and concentration

TL;DR

This paper presents a novel optical cavity resonance-based spectroscopic method for highly precise, non-contact measurement of gas temperature and concentration, surpassing previous techniques in accuracy and pressure range.

Contribution

It introduces a new primary thermometry approach using cavity resonance frequencies and molecular line calculations, achieving unprecedented precision and pressure range extension.

Findings

82 ppm uncertainty in thermometry at 296 K

Sub-permille accuracy in gas concentration measurements

Extends high-precision spectroscopic thermometry over larger pressure ranges

Abstract

We introduce a spectroscopic approach to primary gas thermometry, harnessing precise optical cavity resonance frequencies and ab initio molecular line intensity calculations. By utilizing CO (3-0) vibrational band lines and cavity mode dispersion spectroscopy, we achieve an uncertainty of 82 ppm (24 mK at 296 K) in line-intensity-ratio thermometry (LRT) - over an order of magnitude lower than any previously reported spectroscopic thermometry at gas pressures above 1.2 kPa. This method extends high-precision spectroscopic thermometry across a pressure range an order of magnitude larger than prior techniques, enabling a fully optical, non-contact, and molecule-selective primary amount-of-substance measurement. We further demonstrate sub-permille uncertainty in gas concentration measurements across pressures from 50 Pa to 20 kPa, significantly enhancing the precision and versatility of spectroscopic gas metrology.