Measurement of the Boltzmann constant by the Doppler broadening technique at a 3,8x10-5 accuracy level

TL;DR

This paper reports an optical measurement of the Boltzmann constant using Doppler broadening of ammonia absorption lines, achieving a high precision of 3.8×10⁻⁵, improving accuracy over previous methods.

Contribution

The study introduces an innovative optical technique based on frequency measurement of Doppler profiles to determine the Boltzmann constant with unprecedented precision.

Findings

Achieved a relative uncertainty of 3.8×10⁻⁵ in measuring the Boltzmann constant.

Demonstrated the effectiveness of Doppler broadening technique at high accuracy.

Improved measurement precision by an order of magnitude compared to previous work.

Abstract

In this paper, we describe an experiment performed at the Laboratoire de Physique des Lasers and dedicated to an optical measurement of the Boltzmann constant. With the proposed innovative technique, determining comes down to an ordinary frequency measurement. The method consists in measuring as accurately as possible the Doppler absorption profile of a rovibrational line of ammonia in thermal equilibrium. This profile is related to the Maxwell-Boltzmann molecular velocity distribution along the laser beam. A fit of the absorption line shape leads to a determination of the Doppler width proportional to sqrt(kT) and thus to a determination of the Boltzmann constant. The laser source is an ultra-stable CO2 laser with a wavelength . The absorption cell is placed in a thermostat keeping the temperature at 273.15 K within 1.4 mK. We were able to measure with a relative uncertainty as small as 3.8x10-5, which represents an improvement of an order of magnitude for an integration time comparable to our previous measurement published in 2007 [1]