Implementing the New Kelvin by Laser Spectroscopy

Next autumn, the redefinition of the international System of Units (SI), and in particular of the temperature unit, will be accepted by the General Conference on Weights and Measures (CGPM). Several projects are under way to prepare the new “Mise en pratique” of base units. In this context, we propose an original implementation of the new kelvin based on the measurement of the Doppler broadening of ro-vibrational transitions on ammonia around $\pmb{10}\ \mu \mathbf{m}$ . In this paper, we present the ongoing development of an optical thermometer in the 300 - 430 K range.