Measurement of the Boltzmann constant by the Doppler broadening technique at a 3.8x10(-5) accuracy level

• Published in: Comptes rendus. Physique Vol. 10; no. 9; pp. 883 - 893
• Main Authors: Djerroud, Khelifa, Lemarchand, Cyril, Gauguet, Alexandre, Daussy, Christophe, Briaudeau, Stephan, Darquie, Benoit, Lopez, Olivier, Amy-Klein, Anne, Chardonnet, Christian, Borde, Christian J
• Format: Journal Article
• Language: English
• Published: 01.11.2009
• ISSN: 1631-0705
• DOI: 10.1016/j.crhy.2009.10.020

In this article, we describe an experiment performed at the Laboratoire de physique des lasers and dedicated to an optical measurement of the Boltzmann constant k(B). With the proposed innovative technique, determining k(B) 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 [MathML equation] and thus to a determination of the Boltzmann constant. The laser source is an ultra-stable CO(2) laser with a wavelength l[asymptotic to]10 km. The absorption cell is placed in a thermostat, keeping the temperature at 273.15 K within 1.4 mK. We were able to measure k(B) 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.