Faites connaître cette offre !
Reference : UMR7538-BENDAR-001
Workplace : VILLETANEUSE
Date of publication : Thursday, February 07, 2019
Type of Contract : FTC Scientist
Contract Period : 6 months
Expected date of employment : 1 May 2019
Proportion of work : Full time
Remuneration : Minimum 2600 € gross monthly salary (with no experience)
Desired level of education : PhD
Experience required : Indifferent
The postdoctoral researcher will integrate the 'Metrology, Molecule and Fondamental Tests' team (MMFT) of Laboratoire de Physique des Lasers (LPL). He/She will work under the supervision of Benoît Darquié within the framework of a project dedicated to the 'mise en pratique' of the new kelvin using 'Doppler broadening thermometry' with a direct link to the primary time-frequency standard, in the context of the redefinition of the International System of Units (SI) which will come into effect in 2019.
The redefinition of the SI has been adopted in November 2018 and the new SI will come into effect on the 20/05/2019. This major reform consists in fixing the values of 7 fundamental constants while giving a key role to the primary time-frequency standard, as the 'mise en pratique' of all units requires a link to this standard.
Our objective is to demonstrate the first 'mise en pratique' of the kelvin, within the framework of the new SI, with a direct link to the best French realisation of the frequency unit, the atomic fountains of LNE-SYRTE. The Boltzmann constant kB 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' proposed by the MMFT team of LPL, is currently developed by two teams.
At LPL, the project hinges on the experiment dedicated to the measurement of the Boltzmann constant by laser spectroscopy that has been developed for about a decade [1,2]. It consists in recording a precisely as possible the Doppler profile of an absorption line of gaseous ammonia at thermal equilibrium, the width of which is proportional to the square-root of kBT (T the temperature). Spectroscopy is carried out at about10 µm with a quantum cascade laser (QCL) phase-locked to the secondary standard in this region, a CO2 laser frequency locked to a molecular transition.
One of the objectives is to free us from this secondary standard and to lock the frequency of the CO2 laser to the primary frequency standards available at LNE-SYRTE. We have recently developed a method allowing us to lock any mid-infrared source to a frequency comb stabilised to an ultra-stable 1.55 µm reference of LNE-SYRTE. This signal is calibrated to the atomic fountains of LNE-SYRTE and transferred to LPL using an optical link with active compensation of the propagation-induced phase-noise . A CO2 laser stabilised in this way will then constitute a local oscillator calibrated to the primary standard and spectroscopic measurements will be carried out using the QCL phase-locked to this local oscillator.
Since 2016, the MMTF team of LPL is a partner of the European project 'Implementing the New Kelvin 2' (INK 2) aiming at the 'mise en pratique' of the new kelvin. The role of LPL is to explore the 'Doppler broadening thermometry' method in the 300-430K range. To this end, a new temperature-variable thermostat hosting an absorption cell is under development in collaboration with LNE-CNAM. An important effort has also been carried out on the laser system with the integration of microwave synthesiser developed at LPL for phase-jump-free frequency tuning of the QCL over ~10 GHz.
The postdoctoral researcher will be expected to finalise the spectrometer (thermostat, absorption cell, laser system,…), make it fully operational, and carry out measurements for the 'mise en pratique' of the new kelvin using 'Doppler broadening thermometry' with a direct link to the primary time-frequency standard.
 S Mejri, PLT Sow, O Kozlova, C Ayari, SK Tokunaga, C Chardonnet, S Briaudeau, B Darquié, F Rohart, C Daussy, Measuring the Boltzmann constant by mid-infrared laser spectroscopy of ammonia, Metrologia 52, S314-S323 (2015).
 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, D del Campo, The Boltzmann Project, Metrologia 55, R1 (2018).
 B Argence, B Chanteau, O Lopez, D Nicolodi, M Abgrall, C Chardonnet, C Daussy, B Darquié, Y Le Coq, A Amy-Klein, Quantum cascade laser frequency stabilization at the sub-Hz level, Nature Photon. 9, 456 (2015).
- The successful candidate will first familiarize with the existing experimental setup
He/She will then pursue the ongoing instrumental developments:
- characterization of a large volume (1 m3) thermostat temperature tuneable in the 300-430 K range in collaboration with CNAM and LNE. Stability and homogeneity will be measured, characterized and optimized at the 10 ppm level.
- development of an absorption cell compatible with the thermostat, in paricular in the explored temperature range.
- to reach the best sensitivities, the laser system will be improved in parallel: reduction of the residual amplitude noise using an active feed-back loop; reduction and control of sources of line shape distortions (saturation of the transition, limited detection bandwidth,…); frequency locking of the CO2 to the ultra-stable 1.55 µm frequency reference of LNE-SYRTE using a stabilised frequency comb.
- theoretical and experimental study on the influence of line-mixing effects on temperature retrieval will be performed in collaboration with Università degli studi della Campania Luigi Vanvitelli (Napoli, Livio Gianfrani).
- The postdoctoral researcher will then carry out measurements for the 'mise en pratique' of the new kelvin using 'Doppler broadening thermometry' with a direct link to the primary time-frequency standard.
- The applicant should have a PhD in a relevant area of experimental physics or chemical physics: molecular, atomic physics, spectroscopy, optics and lasers, quantum optics.
He/She will be expected to take an active role in the operation and development of this experimental activity and in all other aspects of the project:
- sourcing and ordering of equipment;
- management, planning and prioritisation of the research activity;
- day-to-day guidance of graduate and undergraduate students;
- development of the collaborations with other project partners;
- attendance at national and international conferences;
- article writing.
This activity takes place at the Laboratoire de Physique des Lasers (UMR 7538 CNRS-Université Paris 13), in Villetaneuse, within the 'Metrology, Molecules and Fundamental Tests' team (MMFT, http://www-lpl.univ-paris13.fr/FR/Equipe-MMT-presentation.awp). The thermometry aspect of the project is conducted in collaboration with LNE-CNAM. For locking the CO2 laser, we benefit from a frequency reference provided by LNE-SYRTE (CNRS-Observatoire de Paris) transmitted to the LPL via an optical fibre. The theoretical and experimental study on the influence of line-mixing effects on temperature retrieval will be performed in collaboration with Università degli studi della Campania Luigi Vanvitelli (Napoli, Livio Gianfrani).
The project is supported by labex First-TF et the Joint Research Project (JRP) H2020 EURAMET EMPIR 'Implementing the New Kelvin 2' (INK 2).
Constraints and risks
We talk about it on Twitter!