LPL - Laboratoire de Physique des Lasers

Metrology, Molecules and Fundamental Tests (MMT)

The group Metrology, Molecules and Fundamental Tests is performing ultra-high resolution molecular spectroscopy in the near and middle infrared and optical frequency metrology. The main experimental projects are the following:


Implementing the new kelvin

Christophe Daussy, Benoît Darquié


The global measurement system, grounded in the international system of units (the SI), is the essential foundation for reliable measurement. Such a measurement system, trans-national and truly global, is necessary for trade, manufacturing, sustaining and improving quality of life. In 2018 the CIPM will introduce the most fundamental change to the SI system ever undertaken since its inception and plans to redefine the SI units in terms of fixed values of fundamental constants. This momentous change needs to be supported with research and documentation to ensure a successful and effective transition takes place. Our project focuses on supporting the redefinition of the SI unit for temperature, the kelvin.


Scientifically this research project is focused on delivering primary thermometry results needed to facilitate an effective unit redefinition by determining an ultra-reliable data set of thermodynamic temperatures from ~1 mK above absolute zero to the copper point (1358 K), with unprecedentedly low uncertainties. These quantities are required to support the implementation of the new kelvin (defined in terms of a fixed value of the Boltzmann constant which is to be agreed by the CIPM in 2018) and to provide a complete thermodynamic data ensemble for any potential future temperature scale.


LPL is internationally renowned for ultra-high resolution vibrational spectroscopy for frequency metrology in the MIR. Its significant advanced infrastructure for laser spectroscopy will be applied to this project (laser sources, mid-infrared optics including home-made electro-optic modulators) as well as experimental setups for accurate studies of laser-molecule interactions in linear and saturated absorption regimes (a 18 m long absorption cell, several 3 m long Fabry Perot cavities, and a 1 m3 ultra-stable thermostat for thermometry applications). The aim of our group is to develop, optimise and test the Doppler Broadening Thermometry (DBT) from the water triple point to the In freezing point, in order to demonstrate its potential and its limitations at high temperatures.


A variable temperature thermostat will be developed at CNAM and LNE (operating in the temperature range 300-430 K). Temperature stability and gradient will be measured and their respective uncertainties will be estimated by LPL in cooperation with CNAM and LNE. We will develop a spectroscopic sample gas cell for ammonia (based on an existing cell operating at room temperature) in the operating temperature range.

At last we will be able to perform temperature measurements by means of DBT in the MIR to support the redefinition of the SI unit for temperature.


Principe de la thermométrie par élargissement Doppler au LPL (DBT)

Principle of the Doppler Broadening Thermometry at LPL


Keywords: fundamental constants, mid-infrared laser spectroscopy, ammonia, Boltzmann constant, molecular spectroscopy, quantum cascade laser


Some references

  1. C. Daussy, M. Guinet, A. Amy-Klein, K. Djerroud, Y. Hermier, S. Briaudeau, Ch.J. Bordé, and C. Chardonnet
    First direct determination of the Boltzmann constant by an optical method,
    Phys. Rev. Lett. 98, 250801, (2007).

  2. C. Lemarchand, M. Triki, B. Darquié, Ch. J. Bordé, C. Chardonnet and C. Daussy,
    Progress towards an accurate determination of the Boltzmann constant by Doppler spectroscopy,
    New J. Phys. 13, 073028 (2011).

  3. M. Triki, C. Lemarchand, B. Darquié, P. L. T. Sow, V. Roncin, C. Chardonnet and C. Daussy,
    Speed-dependent effects in NH3 self-broadened spectra: Towards the determination of the Boltzmann constant,
    Phys. Rev. A 85, Issue 6, 062510 (2012).

  4. F. Rohart, S. Mejri, P. L. T. Sow, Sean K. Tokunaga, C. Chardonnet, B. Darquié, H. Dinesan, E. Fasci, A. Castrillo, L. Gianfrani, C. Daussy,
    Absorption line shape recovery beyond the detection bandwidth limit: application to the precision spectroscopic measurement of the Boltzmann constant,
    Phys. Rev. A 90, 042506 (2014).

  5. S Mejri, PLT Sow, O Kozlova, C Ayari, SK Tokunaga, C Chardonnet , S Briaudeau, B Darquié, F Rohart and C Daussy,
    Measuring the Boltzmann constant by mid-infrared laser spectroscopy of ammonia,
    Metrologia, 52, S314-S323 (arXiv:1506.01828) (2015).

  6. J. Fischer, B. Fellmuth, C. Gaiser, T. Zandt, L. Pitre, F. Sparasci, M. D. Plimmer, M. de Podesta, R. Underwood, G. Sutton, G. Machin, R. M. Gavioso, D. Madonna Ripa, P. P. M. Steur, J. Qu, X. J. Feng, J. Zhang, M. R. Moldover, S. P. Benz, D. R. White, L. Gianfrani, A. Castrillo, L. Moretti, B. Darquié, E. Moufarej, C. Daussy, S. Briaudeau, O. Kozlova, L. Risegari, J. J. Segovia, M. C. Martín and D. del Campo,
    The Boltzmann Project,
    Metrologia 55 (2018) R1–R20 (2018).

  7. C. Daussy,
    Un nouveau système d’unités de mesure pour le XXIe siècle,
    La Recherche 541, 61 (novembre 2018).

  8. C. Daussy,
    Le SI reprend sa température,
    Journal du CNRS, (novembre 2018).




Christophe Daussy

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