Determination of the Boltzmann constant by laser spectroscopy as a basis for future measurements of the thermodynamic temperature

Cyril Lemarchand (1) , Khelifa Djerroud (1) , Benoît Darquié (1) , Olivier Lopez (1) , Anne Amy-Klein (1) , Christian Chardonnet (1) , Christian J. Bordé (1) , Stéphan Briaudeau (2) , Christophe Daussy (1)

1 LPL - Laboratoire de Physique des Lasers
2 LCM - Laboratoire commun de métrologie LNE-CNAM

In this paper, we present the latest results on the measurement of the Boltzmann constant kB , by laser spectroscopy of ammonia at 10 μm. The Doppler absorption profile of a ro-vibrational line of an NH3 gas sample at thermal and pressure equilibrium is measured as accurately as possible. The absorption cell is placed inside a large 1m3 thermostat filled with an ice-water mixture, which sets the temperature very close to 273.15 K. Analysing this profile, which is related to the Maxwell-Boltzmann molecular speed distribution, leads to a determination of the Boltzmann constant via a measurement of the Doppler width (proportional tosqrt( kBT) ). A spectroscopic determination of the Boltzmann constant with an uncertainty as low as 37 ppm is obtained. Recent improvements with a new passive thermostat lead to a temperature accuracy, stability and homogeneity of the absorption cell better than 1 ppm over a day.

Mots clés: fundamental constants; laser spectroscopy; absorption line shape; thermodynamic temperature

Domaines: Physique Quantique [quant-ph]

Cyril Lemarchand, Khelifa Djerroud, Benoît Darquié, Olivier Lopez, Anne Amy-Klein, et al.. Determination of the Boltzmann constant by laser spectroscopy as a basis for future measurements of the thermodynamic temperature. International Journal of Thermophysics, 2010, 31 (7), pp.1347-1359. ⟨10.1007/s10765-010-0755-3⟩. ⟨hal-00431711v4⟩