Month: December 2018
Appel à projets 2019 FIRST-TF en cours
Cet appel à projets vise à soutenir des équipes du réseau FIRST-TF sur des projets ambitieux (projets de recherche, projets en partenariat avec les entreprises, projets de formation ou de diffusion des savoirs vers le public) et à renforcer les collaborations entre ses membres, sur des thématiques axées sur la métrologie Temps Fréquence, sur ses interfaces et sur ses applications.
Cette année, le soutien apporté par FIRST-TF pourra porter uniquement sur du personnel (financement de CDD jeune chercheur, de CDD ingénieur ou technicien, mission doctorale).
Le projet proposé peut être à l’initiative de tout membre de FIRST-TF : laboratoire fondateur ou membre du 2nd cercle.
Date limite de soumission : 14 février 2019
⇒ Plus d’informations et formulaire de demande à télécharger sur la page “Appels d’offre” : http://first-tf.fr/opportunites/appels-doffres/
Pour toute question ou demande d’information relative à cet appel à projets, adressez votre message à ao(at)first-tf.com.
14th of December 2018 (Villetaneuse) – PhD defense of Amine Chaouche Ramdane
Amine Chaouche Ramdane will defend his thesis on 14th of December 2018 at 1:30 pm on the subject “Experimental developments for the characterization and stabilization of semiconductor self-pulsed laser sources for frequency metrology applications”, realized in LPL, under the supervision of Frédéric Du Burck and co-supervised by Vincent Roncin.
The defense will take place in Amphi. D – Institut Galilée at Université Paris 13, 99 av. J.B. Clément 93430 Villetaneuse, in front of a jury composed of Saïda Guellati, Alexandre Shen, Didier Erasme, Loïc Morvan, Pascal Besnard, Daniel Bloch, Frédéric Du Burck, Vincent Roncin.
This PhD thesis focuses on the development of instrumentation for the characterization and stabilization of mode-locked laser sources at 1.55 µm for applications in frequency metrology or stability applications in the field of optical telecommunications.
Two characterization tools based on commercial components were developed with the aim to transfer the frequency stability from a metrological source to tunable sources (ECLD). In both cases, stability transfers over tens of nanometres are demonstrated at the level of 10 -12 . The detailed analysis of those setups shows the limitations resulting from residual amplitude and polarization modulations due to modulators and from polarization fluctuations in fibres. The validation of our approach is achieved by the demonstration of the mode-locked laser frequency stabilization by optical injection leading to the reduction of the width of the injected mode by a factor greater than 1000, the transfer of the injection laser stability to all modes of the comb and the measurement of long term stability of the injected laser modes.
13th of December 2018 (Paris) – PhD defense of Grégoire Vallet
Grégoire VALLET will defend his thesis on 13th of December 2018 at 2:00 pm on the subject “Cavity assisted non destructive detection on a strontium optical lattice clock”, realized in SYRTE, under the supervision of Sébastien Bize and co-supervised by Jérôme Lodewyck.
The defense will take place in room 235A (2nd floor) at ENS, 29 rue d’Ulm 75005 Paris, in front of a jury composed of Caroline Champenois, Robin Kaiser, Jakob Reichel and Morgan Michell.
I will start depicting the current landscape of atom clocks research providing you with the fundamental mechanisms, concepts and tools as well as the issues and challenges of the field, along with a detailed presentation of the working of the strontium optical lattice clock I have been working on during my training.
In a second step I will address the metrological aspect of my activity: evaluations of systematics effects inducing clock frequency shifts and participations to continental scale fiber links clock comparison campaigns. After presenting our most recent uncertainty budget I will expose our preliminary results in exploring one of these effects that we are the first group to report on in the case of strontium clocks and to include in our budget: the clock frequency shift induced by collisions between trapped strontium atoms and hot particles of background residual gas. I will as well expose the model I worked out for addressing this issue which unifies the two incompatible models available in the literature.
Finally I will discuss the research and experimental aspects of my work focused on the achievement of a non destructive detection system of atoms in cavity based on dispersive features of light-matter interaction, aiming at the reduction of two effects detrimental to optical lattice clocks stability: Dick effect and quantum projection noise. I will give as well prospects on the metrological gains expected from such technique.
12th of December 2018 (Besançon) – PhD defense of Grégoire Coget
Grégoire COGET will defend his thesis on 12th of December 2018 at 2:00 pm on the subject “Coherent population trapping Cs cell atomic clock with Auto-Balanced Ramsey interrogation protocol”, realized in FEMTO-ST Institute, under the supervision of Rodolphe Boudot.
The defense will take place at the Amphitheatre gagnepain of ENSMM, in front of a jury composed of Carlos Garrido Alzar, Martina Knoop, François Nez, François-Xavier Esnault, Rodolphe Boudot, Vincent Giordano.
This thesis reports a high-performance Cs vapor cell atomic clock based on coherent population trapping (CPT).
This simple-architecture clock prototype combines a DFB diode laser (895 nm, Cs D1 line), a fibered electro-optical modulator driven by an ultra-low phase noise microwave frequency synthesizer, an acousto-optical modulator, a Michelson system, a buffer gas filled Cs vapor cell and FPGA-based low noise electronics.
The clock combines an optimized CPT pumping scheme, named push-pull optical pumping (PPOP), and a Ramsey-like pulsed interrogation, allowing the detection of high-contrast Ramsey-CPT fringes.
During this thesis has been implemented and adapted for this vapor-cell CPT clock, a novel interrogation protocol recently proposed by PTB for optical clocks, named Auto-Balanced Ramsey (ABR). This method, aiming to eliminate probe-induced frequency shifts, is based on the extraction of two error signals derived from two successive Ramsey sequences with different dark periods. The first feedback loop uses the error signal generated by the short Ramsey sequence to apply a phase-step correction to the local oscillator during the dark time that nulls the probe-field induced frequency shift. The second loop provides the means to stabilize the local oscillator frequency using the error signal derived from the long Ramsey sequence.
This ABR-CPT protocol, improved further with symmetrization (SABR-CPT), has allowed to reduce drastically the sensitivity of the clock frequency to laser power variations, by a factor 80 in comparison with a standard Ramsey-CPT interrogation. This CPT clock exhibits today the fractional frequency stability level of 2 10-13 τ-1/2, with best demonstrated mid-term stability in quiet conditions at the level of 2.5 10-15 at 10 000 s.
Annex laser spectroscopy studies in Cs microfabricated cells were also performed in this thesis. We note the preliminary demonstration of a frequency-stabilized laser using dual-frequency sub-Doppler spectroscopy in a Cs microcell, exhibiting an encouraging fractional frequency stability lower than 2 10-12 at 1 s. These short-term stability performances are 10 times better than those of microwave CPT-based chip-scale atomic clocks.
12th of December 2018 (Besançon) – PhD defense of Jérémy Bon
Jérémy BON will defend his thesis on 12th of December 2018 at 10:30 am on the subject “Résonateurs à ondes acoustiques de volume piégées à très basses températures : Application à l’optomécanique”, realized in FEMTO-ST Institute, under the supervision of Serge Galliou.
The defense will take plac eat the Amphitheatre Jules Haag of ENSMM, in front of a jury composed of Ludovic Bellon, Bernard Bonello, Pierre-François Cohadon, Gianpietro Cagnoli, Bernard Dulmet, Serge Galliou et Roger Bourquin.
For a few years, the Time and Frequency department in FEMTO-ST Insitute has been leading research about the behavior of Bulk Acoustic Wave (BAW) trapped in quartz crystal at cryogenic temperatures (near 4K).
The measured quality factor are around a few billions at few tens of MHz for such temperatures. Acoustical quartz cavities are therefore good candidates for ultrastable cryogenic frequency sources.
The work presented here is in the natural continuation of the research cited above. They aim at strenghtening the interest for quartz crystal, but also to consider alternative solutions with non-piezoelectric material with very-low acoustical losses, for which optical excitation is an option.
The following work can be summed up in three main parts:
– The first part is about the determination of a quartz crystal cut for which an turnover point exists in the frequency-temperature curve in the cryogenic region. Indeed, it is not enough to barely control the temperature in an ultrastable frequency source. Such an turnover point needs to be the operation point for thermal regulation. Searching a compensated cut arose the need for a preliminary measurements campaign of thermal coefficients of elastic coefficients of the material, which were unknown at low temperature.
It was then possible, based on these coefficients, to calculate and even realize a cut fulfilling the required condition.
– The second part had the objetive to demonstrate conceptually that using a quartz acoustical cavity as an optical cavity was feasable. In its basic scheme, a BAW quartz resonator is plano-convex (to ensure the trapping of the acoustic wave) and has electrodes (metal-made to ensure electrical excitation) deposited on each face. It has been demonstrated, both theoretically and experimentally, that such a geometry works fine as an optical cavity, with its corresponding advantages and limitations. This scheme is used for the optomechanical coupling discussed in the third part and constitutes the very base for more efficient optomechanical devices.
– The third part is dedicated to the evaluation of how efficient will such devices be while functioning at cryogenic temperature. A theoretical quantitication of the optomechanical coupling that these cavities might reach is also presented.
Producing an optomechanical cavity will allow avoiding the physical constraints imposed by the use of a cryogenerator and will open the way to the study of non-piezoelectric material with very low mechanical losses, similar or even lower than that of quartz.
This kind of experimentation also answers to the needs of other research teams working on quantum optomechanics or hybrid quantum systems (LKB, UWA, …) with which collaborations are currently being held.
11th of December 2018 (Besançon) – PhD defense of Etienne Vaillant
Etienne VAILLANT will defend his thesis on 11th of December 2018 on the subject “Contribution à la mesure du bruit propre de résonateurs MEMS”, realized in FEMTO-ST with Fabrice Sthal et Joël Imbaud.