Determination of the Boltzmann constant by laser spectroscopy as a basis for future measurements of the thermodynamic temperature

In this paper, we present the latest results on the measurement of the Boltzmann constant kB, by laser spectroscopy of ammonia at 10 ?m. The Doppler absorption profile of a ro-vibrational line of an NH3 gas sample at thermal and pressure equilibrium is measured as accurately as possible. The absorption cell is placed inside a large 1m3 thermostat filled with an ice-water mixture, which sets the temperature very close to 273.15 K. Analysing this profile, which is related to the Maxwell-Boltzmann molecular speed distribution, leads to a determination of the Boltzmann constant via a measurement of the Doppler width (proportional tosqrt(kBT)). A spectroscopic determination of the Boltzmann constant with an uncertainty as low as 37 ppm is obtained. Recent improvements with a new passive thermostat lead to a temperature accuracy, stability and homogeneity of the absorption cell better than 1 ppm over a day

Measurement of the Boltzmann constant by the Doppler broadening technique at a 3,8x10-5 accuracy level

In this paper, we describe an experiment performed at the Laboratoire de Physique des Lasers and dedicated to an optical measurement of the Boltzmann constant. With the proposed innovative technique, determining 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 sqrt(kT) and thus to a determination of the Boltzmann constant. The laser source is an ultra-stable CO2 laser with a wavelength . The absorption cell is placed in a thermostat keeping the temperature at 273.15 K within 1.4 mK. We were able to measure 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 [1

A revised uncertainty budget for measuring the Boltzmann constant using the Doppler Broadening Technique on ammonia

We report on our on-going effort to measure the Boltzmann constant, kB, using the Doppler Broadening Technique. The main systematic effects affecting the measurement are discussed. A revised error budget is presented in which the global uncertainty on systematic effects is reduced to 2.3 ppm. This corresponds to a reduction of more than one order of magnitude compared to our previous Boltzmann constant measurement. Means to reach a determination of kB at the part per million accuracy level are outlined

with nanosecond time resolution

An optical setup for the measurement of acoustic shock waves is demonstrated experimentally. This sensor, which is based on surface plasmon excitation, provides ns time resolution as well as mm lateral resolution. Initial experiments with laser-induced plasma generation in a water cell already show that in a simple geometry high lateral resolution gives new insight into the ongoing processes

Méthodes d’Auto-Validation Pour Thermocouples à Haute Température

Une des grandes difficultés dans l’utilisation de thermocouples à haute température (au-delà de 1000 °C) est de maîtriser leur dérive. Soumis à leurs températures limites de fonctionnement, les thermocouples ont tendance à dériver, principalement à cause de recombinaisons structurelles inhérentes au recuit thermique. Ceux-ci sont également exposés à des pollutions depuis leurs milieux de mise en œuvre, ce qui peut conduire à des hétérogénéités de composition sur la longueur des thermo-éléments, altérant ainsi leurs pouvoirs thermoélectriques. La solution proposée est d’embarquer, voire intégrer un point-fixe de temperature de référence au thermocouple, permettant ainsi un étalonnage in situ du capteur lorsque le procédé permet de réaliser la transition de phase (fusion et/ou congélation) du matériau point-fixe. Cet article présente quelques méthodes et techniques en cours de développement au LNE-Cnam visant à mettre en pratique des méthodes d’auto-validation de thermocouples à haute température, sous atmosphères neutres et oxydantes

Implementing the new kelvin by molecular precision spectroscopy

International audienceNext autumn, the redefinition of the international System of Units (SI) will be accepted by the General Conference on Weights and Measures. This major reform will establish a new definition of units in terms of a set of 7 defining constants. The temperature unit, the kelvin, the definition of which is currently based on the triple point of water (TPW), will for example be redefined by fixing the value of the Boltzmann constant kB. For the implementation of the new kelvin, various primary thermometry methods are currently being developed such as Doppler-broadening thermometry (DBT), acoustic gas thermometry, Johnson noise thermometry, dielectric constant gas thermometry, etc... We have previously proposed and developped the DBT method and have used it to demonstrate an accurate determination of kBa,b. Once kB fixed in the new SI, DBT will become a primary spectroscopic method for thermodynamic temperature measurements and thus for the implementation of the new kelvin. DBT is based on the precise measurement of the Doppler broadening of absorption line of a gaz phase atomic or molecular species, an ammonia ro-vibrational transition in the mid-infrared range (∼ 10μm) in our case, combined with some highly accurate modeling of the line profile. We are currently developing DBT in thetemperature range 300-430K, in order to demonstrate its potential and study its limitations beyond the temperature of the TPW. We will present our progress towards temprature measurements with uncertainties at the 25ppm level. The existing set-up (previously used for the determination of kB) has been upgraded. We have placed the spectroscopic cell in a variable thermostat, the temperature stability and gradient of which has been characterized. We have also improved our mid-infrared spectrometer to investigate, in particular the influence of the line-mixing on the temperature measurement accuracy

Amélioration des références et dissémination dans le domaine des hautes températures et de la pyrométrie optique au LNE-Cnam

Parmi les missions dévolues au Laboratoire Commun de Métrologie LNE-Cnam figurent la réalisation, l’amélioration et la dissémination de l’unité de température, le kelvin, sur tout le domaine de température. Dans le département « hautes températures et pyrométrie optique » cela concerne la thermométrie de contact au-dessus de 1000 °C et la pyrométrie optique sur tout le domaine de température. L’objectif de cet article est de permettre une vue d’ensemble des activités de recherche et d’étalonnage dans ce department ainsi que les projets transverses dans lesquels l’équipe est impliquée au-delà des limites des départements et des pôles du laboratoire. L’accent sera mis en particulier sur notre implication dans les projets européens de recherche concertée (JRP) qui nous engagent sur des durées de plusieurs années avec nos collègues européens sur des enjeux importante pour l’industrie et la société, tels que l’énergie, le système international d’unités et l’aide à l’industrie

Experimental assessment of methods of dissemination of the thermodynamic temperature at the highest temperatures

In the frame of the European Metrology Research Programme (EMRP)-funded joint research project “Implementing the new kelvin” one work package is devoted to the assessment of two different methods of dissemination of the thermodynamic temperature. These two methods are the dissemination via high temperature fixed points (HTFP) with assigned thermodynamic temperatures and the dissemination by radiometers or radiation thermometers calibrated in terms of thermodynamic temperature. To achieve a thorough assessment of these two distinct dissemination methods two dissemination exercises were organised in the form of comparisons. In one case the circulating artefacts were off-the-shelf high-temperature fixed point cells with transition temperatures ranging from 1324 °C to 2474 °C, in the other case absolutely calibrated pyrometers and filter radiometers were compared in the temperature range 1000 °C to 2500 °C. This work showed that both schemes were achievable with competing advantages and drawbacks and would most probably help disseminating thermodynamic temperature in the future at the level of 1 K to 2 K uncertainty over the whole temperature range