Doppler broadening thermometry based on cavity ring-down spectroscopy

TL;DR

This paper presents a cavity ring-down spectroscopy-based Doppler broadening thermometry instrument that achieves high precision in measuring the Boltzmann constant by reducing collision effects and analyzing spectral linewidths.

Contribution

It introduces a novel CRDS-based DBT method that improves measurement precision and reduces collision influence compared to traditional absorption techniques.

Findings

Achieved 6 ppm statistical uncertainty in linewidth measurement.

Reproducibility better than 10 ppm over several hours.

Demonstrated feasibility for ppm-level temperature measurement.

Abstract

A Doppler broadening thermometry (DBT) instrument is built based on cavity ring-down spectroscopy (CRDS) for precise determination of the Boltzmann constant. Compared with conventional direct absorption methods, the high-sensitivity of CRDS allows to reach a satisfied precision at lower sample pressures, which also reduces the influence due to collisions. By recording the spectrum of C$_2$H$_2$ at 787 nm, we demonstrate a statistical uncertainty of 6 ppm (part per million) in the determined linewidth values by several hours' measurement at a sample pressure of 1.5 Pa. The influence on the spectroscopy-determined temperatures has been investigated, including the "hidden" weak lines overlapped with the selected transition for DBT measurements. The reproducibility has also been examined to be better than 10 ppm, and it indicates that the instrument is feasible for DBT measurement toward a precision at the ppm level.