Mise en Pratique of the New Kelvin Using Doppler Broadening Thermometry with a Direct Link to the Primary Frequency Standards

We aim to demonstrate the first mise en pratique of the kelvin, within the framework of the new International System of Units (SI), with a direct link to the atomic fountains of LNE-SYRTE laboratory, the French time-frequency metrology institute. The Boltzmann constant being fixed in the new SI, the mise en pratique of the kelvin can be cast as a frequency measurement. One method considered, Doppler Broadening thermometry (DBT), originally proposed and initially demonstrated at Laboratoire de Physique des Lasers is being developed by us and others. We report our recent efforts towards implementing DBT with a direct link to the primary frequency standard in the 300–430K range to demonstrate its potential.