First direct determination of the Boltzmann constant by an optical method

International audienceWe have recorded the Doppler profile of a well-isolated rovibrational line in the ν2 band of 14NH3. Ammonia gas was placed in an absorption cell thermalized by a water-ice bath. By extrapolating to zero pressure, we have deduced the Doppler width which gives a first measurement of the Boltzmann constant, kB, by laser spectroscopy. A relative uncertainty of 2x10-4 has been obtained. The present determination should be significantly improved in the near future and contribute to a new definition of the kelvin

Realisation of the ITS-90 and thermodynamic temperature measurements above 960 °C using a monochromator-based radiance comparator

International audienceAt LNE-Cnam, the International Temperature Scale of 1990 (ITS-90) and thermodynamic temperature measurements above the silver point, are carried out with a radiance comparator. This instrument is, more generally, devoted to any radiance comparison in temperature range from the ambient to 3000 °C. The instrument developed in the early 1990s at LNE-Cnam has the advantage of being completely adjustable. Compared to compact radiation thermometers based on lenses and a narrow-band interference filter, the radiance comparator is only made of gold coated mirrors and a Czerny-Turner monochromator to select the spectral bandwidth. The instrument offers the possibility to tune the geometric extent and the slit scattering function. In return, the radiance comparator is a complex instrument that requires a complete and a regular characterisation at the highest level of accuracy. In the first part, this paper describes the instrument and its operating principle. In a second part, a complete study of the wavelength calibration, the slit scattering function, size of source effect, out-ofband transmittance, linearity and other main sources of uncertainty are presented and discussed. Their associated uncertainties are estimated separately and are grouped together to give an example of propagation of uncertainties when realising the ITS-90

The synthetic double wavelength technique: a simple robust method for thermodynamic temperature determination

International audienceThis paper describes a new relative technique developed at LNE-Cnam, for the determination of the thermodynamic temperature of blackbodies without recourse to a radiometric reference. This technique is referred to as the 'synthetic double wavelength technique' (SDWT) as it is considered to be a particular case of the 'double wavelength technique' (DWT). It offers a new experimental technique for the determination of the thermodynamic temperature at high temperature and as such a new means for the mise-en-pratique of the new definition of the kelvin achievable by any national metrology institute provided a multi-wavelength radiation thermometer combining large and narrow bandwidths is available. In this work, a first experimental implementation of this technique based on a wavelength-tuneable spectroradiometer providing both narrowband and broadband signals with the particularity of the broadband signal being virtually synthesised from the spectral distribution of the narrowband signals sampled over a wide spectral range. SDWT determination of the thermodynamic temperature of a blackbody at 2760 K was performed with a level of uncertainty that confirms the promising capabilities of this technique

Implementing the New Kelvin by Laser Spectroscopy

International audienceNext 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 10 μm. In this paper, we present the ongoing development of an optical thermometer in the300 K-430 K range

Recent developments in sub-doppler spectroscopy in a thin cell

the original paper published as J Phys IV 10, Pr8-145 (2000), does not seem available on-lineInternational audienceWe report on the special sub-Doppler features of high-resolution spectroscopy in a thin cell, in conditions when the atomic free path is anisotropic as due to the special cell geometry. The most recent developments include linear spectroscopy under normal incidence, an extension to transition between excited states, and the observation of atoms flying under grazing incidence in a pump-probe scheme with spatially separated beam

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

International audienceWe 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

Photonic and Optomechanical Thermometry

International audienceTemperature is one of the most relevant physical quantities that affects almost all processes in nature. However, the realization of accurate temperature standards using current temperature references, like the triple point of water, is difficult due to the requirements on material purity and stability of the environment. In addition, in harsh environments, current temperature sensors with electrical readout, like platinum resistors, are difficult to implement, urging the development of optical temperature sensors. In 2018, the European consortium Photoquant, consisting of metrological institutes and academic partners, started investigating new temperature standards for self-calibrated, embedded optomechanical sensor applications, as well as optimised high resolution and high reliability photonic sensors, to measure temperature at the nano and meso-scales and as a possible replacement for the standard platinum resistant thermometers. This article presents an overview of the results obtained with sensor prototypes that exploit photonic and optomechanical techniques for sensing temperatures over a large temperature range (5 K to 300 K). Different concepts are demonstrated, including ring resonators, ladder-like resonators and suspended membrane optomechanical thermometers, highlighting initial performance and challenges, like self-heating that need to be overcome to realize photonic and optomechanical thermometry applications

The Boltzmann Project

The International Committee for Weights and Measures (CIPM), at its meeting in October 2017 followed the recommendation of the Consultative Committee for Units (CCU) on the redefinition of the kilogram, ampere, kelvin and mole. For the redefinition of the kelvin the Boltzmann constant will be fixed with the numerical value 1.380 649x10-23 JK-1. The relative standard uncertainty to be transferred to the thermodynamic temperature value of the triple point of water will be 3.7x10-7, corresponding to an uncertainty in temperature of 0.10 mK, sufficiently low for all practical purposes. With the redefinition of the kelvin the broad research activities of the temperature community on the determination of the Boltzmann constant have been very successfully completed. In the following, a review of the determinations of the Boltzmann constant k important for the new definition of the kelvin and performed in the last decade is given