Accurate determination of the Boltzmann constant by Doppler spectroscopy: Towards a new definition of the kelvin
1 CNRS, UMR 7538, LPL, 93430 Villetaneuse, France
2 Université Paris 13, Sorbonne Paris Cité, Laboratoire de Physique des Lasers, 93430 Villetaneuse, France
3 Laboratoire National de Métrologie et d'Essais-Système de Références Temps-Espace, UMR 8630 Observatoire de Paris, CNRS, UPMC, 75014 Paris, France
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Accurate molecular spectroscopy in the mid-infrared region allows precision measurements of fundamental constants. For instance, measuring the linewidth of an isolated Doppler-broadened absorption line of ammonia around 10 μm enables a determination of the Boltzmann constant kB. We report on our latest measurements. By fitting this lineshape to several models which include Dicke narrowing or speed-dependent collisional effects, we find that a determination of kB with an uncertainty of a few ppm is reachable. This is comparable to the best current uncertainty obtained using acoustic methods and would make a significant contribution to any new value of kB determined by the CODATA. Furthermore, having multiple independent measurements at these accuracies opens the possibility of defining the kelvin by fixing kB, an exciting prospect considering the upcoming redefinition of the International System of Units.
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