Measuring the Boltzmann constant by mid-infrared laser spectroscopy of ammonia

TL;DR

This paper discusses improvements in mid-infrared laser spectroscopy of ammonia aimed at precisely measuring the Boltzmann constant, focusing on enhanced spectrometer components, refined data analysis, and systematic effect mitigation.

Contribution

It introduces advanced spectroscopic techniques and analysis methods to improve the accuracy of Boltzmann constant measurement via Doppler broadening of ammonia.

Findings

Use of phase-stabilized quantum cascade laser improves spectral stability.

Refined lineshape analysis enhances parameter estimation accuracy.

Systematic effects are identified and strategies for mitigation are outlined.

Abstract

We report on our ongoing effort to measure the Boltzmann constant, $k_B,$ using the Doppler broadening technique on ammonia. This paper presents some of the improvements made to the mid-infrared spectrometer including the use of a phase-stabilized quantum cascade laser, a lineshape analysis based on a refined physical model and an improved fitting program 2 increasing the confidence in our estimates of the relevant molecular parameters, and a first evaluation of the saturation parameter and its impact on the measurement of k B. A summary of the systematic effects contributing to the measurement is given and the optimal experimental conditions for mitigating those effects in order to reach a competitive measurement of $k_B$ at a part per million accuracy level are outlined.