Defenses – Seminars


  • 8 December 2016 (Palaiseau) - Thesis defense of Paul Dumont : "Dual-frequency optically-pumped semiconductor laser for atomic clocks based on coherent population trapping of cesium atoms"

    Paul Dumont will defend his thesis on Dec. 8th, 2016 at 13:30, Institut d’Oprique (Palaiseau) on the subject “Dual-frequency optically-pumped semiconductor laser for atomic clocks based on coherent population trapping of cesium atoms”. This work has been realized at LCF – Laboratoire Charles Fabry under the supervision of Gaelle Lucas-Leclin and Patrick Georges. This thesis has been co-funded by FIRST-TF.

     

    Abstract : Atomic clocks using the coherent population trapping (CPT) technic are ex-
    cellent candidates to obtain frequency references that are stable, compact and with a low power
    consumption. In the case of cesium atomic clocks, this technic require a dual-frequency laser
    eld either at 895 nm (D1 transition) or 852 nm (D2 transition) and whose frequency dierence
    is equal to 9.19 GHz, the frequency splitting between the two hyperne levels of the fundamen-
    tal state. Here we present a new concept for generating this type of laser eld using a unique
    dual frequency and optically-pumped laser with a dual-polarized emission.
    In this manuscript, we study the conception of such a laser source with an emission tunable
    at the D2 transition of cesium atoms. We detail the design of the intracavity elements and the
    semiconductor active structure. Then we describe the experimental set-up and characterization
    of a rst prototype. We present the stabilization set-up of the laser based on two dierent
    servo-loops, one used to lock the optical frequency onto the cesium transition and the other
    to lock the frequency dierence onto the frequency generated by a local oscillator. We report
    a complete simulation and characterization of the main laser noises: the laser intensity noise,
    the optical frequency noise, and the phase noise of the radiofrequency signal generated by the
    beatnote of the two laser modes. We show the rst experimental results of coherent population
    trapping obtained with the prototype. Finally we establish a noise budget of a CPT atomic clock
    by estimating the impact of each laser noises. After we identify the system limits, we propose
    dierent ways to improve the dual-frequency which rely on the reduction of the intensity noise
    and the modication of the semiconductor structure design.


  • 30 november 2016 (Paris) - Seminar of Frank Quinlan (NIST, USA) : "Optical to RF frequency generation with optical frequency combs"

    Seminar of Labotory Kastler Brossel,  will be held on Wednesday November 30 at 13:45  in room 2 of the Collège de France,  Paris

     

    The most frequency-stable electromagnetic radiation is now produced optically, with stable reference cavities demonstrating fractional frequency instabilities below 10^-16 at 1 second and optical clocks reaching 10^-18 at 10^4 seconds. This talk will cover recent work at NIST using optical frequency combs to transfer this stability across the optical domain at the level of 10^-18 at 1 second, as well as into the RF, microwave, and mm-wave domains at the level of 10^-15 to 10^-17 at 1 second. In addition to the optical frequency combs themselves, elements of compact ultrastable optical cavities, high-speed photodetection and broadband electronic synthesis will also be discussed.


  • 29 november 2016 (Besançon) - Thesis defense of Nikolay Vorobiev"Miniaturization of OCXO oscillators for space applications"

    Defense  realized at FEMTO-ST, which will be partly public, will take place on Tuesday, 29 of november 2016 at 14:00  in Amphithéatre Mesnage, ENSMM, 26 rue de l’Epitaphe, Besançon.

     

    This thesis presents the work on designing a miniature temperature controlled crystal oscillator (required volume is 1 cm3). TTC (Telemetry, Tracking and Control) equipment which is used in microsatellites (as Myriades) has a very important volume (8 liters). 8 times lower volume equipment (1 liter) is planned for pico and nano satellites. Therefore, a significant reduction of volume and consumption for equal performance is necessary. Redesign is required for all components of equip-ment items including micro-oscillator, as in volume as at the level of energy consumption. Preliminary studies have served to define the resonator adapted to satisfy the request stability specifications. Thermal simulation of an OCXO oscillator model (Oven Con-trolled Xtal Oscillator) has permitted to achieve a good understanding of heat transfer into the device. Reducing heat loss and increases the thermal stability of resonator were major challenges. Thermal expansion of the resonator causes mechanical stresses in its mountings and shifts the resonance frequency. A silicon MEMS has designed for supporting the resonator by using thermomechanical simulations. This support is compatible with the constraints of low consumption and heat sensitivity retaining good impact resistance. As regards electronics, an ASIC chip which is used during many years has characterized with the purpose to obtain the digital model. This study has revealed the limiting factors of the oscillator performance. Also it has allowed to provide remedial solutions. The ASIC using was rejected in favor of the solution operating with commercial electronic components (at least temporarily). Finally, a miniature demonstrator of physical module was assembled and characterized. The measuring results show that demonstrator consumption remains below the required specification. The importance of the participation of radiation within the thermal exchanges has also validated experimentally.

    Keywords: acoustic resonator, quartz, OCXO oscillator, phase noise, thermal control, force-frequency effect, thermomechanical modeling, miniaturization.

     



  • 18 november 2016 (Paris) - Thesis defense of Satyanarayana BADE : "Propagation of atoms in a magnetic waveguide on a chip"

    Defense on Thursday, 18 of november 2016 at 14:00 in Room “Salle des séminaires” of the “Institut d’Astrophysique de Paris” (IAP).

    This entrance will take place : 77 avenue Denfert Rochereau – 75014 Paris

    The Thesis will be in english

     

    In this thesis we study the propagation of atoms in a magnetic toroidalwaveguide, with the aim of developing an inertial sensor. Here, we present differentstrategies to create the waveguide on an atom chip for a guided Sagnac atominterferometer. We devised three solutions which can be achieved using the samewire configuration. They use the current modulation technique, from a new pointof view, which simultaneously tackles the problem of wire corrugation and spindependent Majorana atom losses. The effect of the multimode propagation of theatoms in the guide is also quantified in this thesis. Using a simple model, we coveredthe propagation of noninteracting ultracold and thermal gases. We identifiedthe operating conditions to realize a cold atom interferometer with a large dynamicrange essential for applications in inertial navigation. Experimentally, the thesisdescribes the realisation and characterisation of the cold atom source close to agold coated substrate, as well as the implementation and the characterisation of theatom detection systems.


  • 4 november 2016 (Paris) - Thesis defense of Pierre Gillot : "Long term stability of a cold atom gravimeter and limit of the rejection technic of systematics effects"

    Defense on Thursday, 4 of november 2016 at 14:00 in Room “Salle des séminaires” of the “Institut d’Astrophysique de Paris” (IAP).

    This entrance will take place : 77 avenue Denfert Rochereau – 75014 Paris

    Work installed at the LNE at Trappe under the supervision Franck Pereira Dos Santos and Sébastien Merlet

    This thesis aims at pushing the performances of the atom gravimeter CAG developed at SYRTE. This instrument uses atom interferometry to measure the local gravity acceleration of a free falling 87Rb cold atomic cloud. The improvements of the Raman power control and parameters such as those driving the detection are presented in this thesis. The initial position of the cloud, its mean velocity, its ballistic expansion into the Raman beams and thus their evolution, are important parameters which affect the performances of the CAG. The resulting coupling inhomogeneities modify the symmetry of the sensitivity function of the interferometer and make it sensitive to constant Raman detuning. Moreover, the Raman detuning in a Doppler way cannot be canceled by our rejection technic of systematic effects. The asymmetry of the sensitivity function has been measured and a method is demonstrated to cancel it. Several comparisons between the CAG and different gravimeter types have been performed and their results are developed. The international comparison of absolute gravimeters CCM.G-K2 confirms the CAG accuracy budget. It reveals an Allan standard deviation of 5.710-9g/Hz1/2. In the end, a one month common view measurement with a superconducting gravimeter iGrav is studied. The determination of the iGrav scale factor at the level of 0.1% in a single day and 0.02% in less than a month is obtained with this long measurement. The Allan standard deviation of the gravity residual signal is 610-11g in 12h measurement time.


  • 3 november 2016 (Paris) - Thesis defense of Cyrille SOLARO "TRAPPED ATOM INTERFEROMETERS : FROM LOW TO HIGH DENSITY REGIME"

    Defense  on Thursday, 3 of november 2016 at 14:00  in Room “Salle des séminaires” of the “Institut d’Astrophysique de Paris” (IAP).

    This entrance will take place :  77 avenue Denfert Rochereau – 75014 Paris

    The Defense will be made in french.

    Work realized at the SYRTE  under the supervision Franck Pereira Dos Santos

    This thesis presents the recent progress on the FORCA-G (FORce de CAsimir et Gravitation
    à courte distance) experiment which aims at measuring short range forces between an atom,
    trapped in a vertical optical lattice, and a mirror. Stimulated Raman transitions are used to
    induce coherent transport between adjacent lattice sites to perform atom interferometry in order to measure with very high sensitivity, shifts in the Bloch frequency ÜB, which is the potential increment between two lattice sites. For low atomic densities, we demonstrate a local force sensor with state-of-the art relative sensitivity on the Bloch frequency of 1.8 × 10−6 at 1 s. The recent use of evaporative cooling, in order to increase the number of atoms per well, allows to work the experiment with much denser atomic clouds where atom interactions cannot be neglected. At densities of 10^11 − 10^12 at/cm3, it is shown that a spin self-rephasing mechanism competes with the spin-echo technique. The impact of the former mechanism onto the contrast and the measured frequency is studied in an interferometer where the two partial wave packets perfectly overlap. First measurements are then performed in a regime where the two partial wave packets are spatially separated. They show a different behavior that remains to be modelled.
    Finally, it is shown that the measurement protocol allows to greatly reduce collisional shifts:
    atom interactions limit the sensitivity of the local force sensor without limiting its accuracy.
    Key-words : atom interferometry, short-range forces, ultracold atoms, inertial sensor, optical
    lattice, spin self-rephasing

     


  • 7 October 2016 (Paris) - Thesis defense of Clément COURVOISIER "Condensat de Bose-Einstein par refroidissement évaporatif dans un piège dipolaire pour la métrologie par interférométrie atomique"

    Defense  on Friday, 7 of October 2016 at 14:00 at UPMC – 4 Place Jussieu – 75005 Paris

     

    This research work fulfilled as part of my PhD project involved to design, build and characterise a new experimental setup based on an atom source by evaporative cooling in an optical dipole trap. It goes after the improvement of the uncertainty on the measurement of  the ratio h/m between Planck’s constant and the rubidium atom mass, reducing the Gouy phase and wavefront curvature.
    In a first step we have studied several optical configurations to optimise the dipole trap loading: the 50 W beam at 1070 nm is shaped in a double 93 μm waist reservoir and one crossed 20 μm waist dimple. After having optimised and caracterised the evaporative process, we obtained one Bose-Einstein condensate.
    Furthermore, for Raman interferometry, we set up a new laser system at 1560 nm based on frequency doubling. We developed a double cervo loop: on the one hand, it allows to phase lock the two laser sources, and on the other hand to correct phase noise accumulated in fibered amplifiers.
    Today, our new experimental setup is ready to perform atom interferometry on a Bose-Einstein condensate.


  • 30 september 2016 (Paris) - Thesis defense of Konstantin OTT : "Towards a squeezing-enhanced atomic clock on a chip"

    Defense  on Friday, 30 of September 2016 at 14:00 –  in Room “Salle des séminaires” of the “Institut d’Astrophysique de Paris” (IAP) – 98 bis Boulevard Arago – 75014 Paris

    Work realized at the SYRTE  and the Laboratoire Kastler Brossel under the supervision Peter ROSENBUSCH and Jakob REICHEL

    In front of a jury composed of Philippe Bouyer – Matthias Keller – Agnès Maitre – François-Xavier Esnault – Tilo Steinmetz et Jean-Marc Lasage

    This defense will be in english.

     

    This thesis describes the conception and construction of an “entanglement-enhanced”

    trapped atom clock on an atom chip (TACC). The key feature of this new experiment

    is the integration of two optical Fabry-Pérot micro resonators which enable generation

    of spin-squeezed states of the atomic ensemble via atom-light interactions and non-

    destructive detection of the atomic state.

    It has been shown before that spin-squeezed states can enhance the metrological

    performance of atomic clocks, but existing proof-of-principle experiments have not yet

    reached a metrologically relevant level of precision. This is the first goal of the new

    setup.

    To retain the compactness and stability of our setup, we chose the optical resonator

    to be a fiber Fabry-Pérot (FFP) resonator where the resonator mirrors are realized on

    the tip of optical fibers. To meet the requirements of our experiment, a new generation

    of FFP resonators was developed in the context of this thesis, demonstrating the longest

    FFP resonators to date. For this purpose, we developed a “dot milling” procedure using

    a focused CO2-laser that allows shaping of fused silica surfaces with unprecedented

    precision and versatility. Beyond the TACC experiment these long FFP resonators

    open up new applications in other fields as in the ion trapping community or for

    frequency filtering.

    Incorporating optical resonators in the TACC system necessitates a new atom chip

    design, allowing transportation of the atom cloud into the resonator. We present the

    design and the fabrication of this atom chip.

    The completed setup will enable investigations of the interplay of spin-dynamics in

    presence of light mediated correlations and spin-squeezing at a metrologically relevant

    stability level of 10^(−13) at 1 s.

     


  • 10 June 2016 (Paris) – Thesis defense of Stéphane TREMINE : "Study of Cesium atoms cooling in a 3D speckle laser field and realization of a compact atomic clock".

    Defense  on Friday, 10 of June 2016 at 10:00 –  à l’Observatoire de Paris


  • 6 June 2016 (Besançon) – Thesis defense of Alexandre DIDIER : "Development of ultra-stable Fabry-Perot cavities for new generation optical frequency standards".

    Defense  on Monday, 6 of June 2016 at 10:00 –  Amphi JJ. Gagnepain, Femto-ST, Besançon


  • 27 jan. 2016 (Paris) - "Study and realization of a new spatio-temporal reference system based on inter-satellite links in a GNSS constellation"

    Defense  on Wednesday, 27 of January 2016 at 14:30 –  l’amphithéâtre de l’IAP, Observatoire de Paris

    Work accomplished in  SYRTE under the supervisionPeter WOLF and Pacôme DELVA

    The accuracy reached by the Global Navigation Satellite Systems (GNSS) is critically important for many scientific applications such as geodetic point or satellite positioning, space-time reference frame realization, clocks synchronization or the study of the links to probe the atmosphere. One option for improving the system accuracy is the use of inter-satellite pseudo-range measurements, so called inter-satellite links (ISL). Several studies have shown the qualitative interest of ISL but do not allow to efficiently measure the quantitative impact of this new technology on space-time positioning. In this thesis, we present a differential study between a standard system (with standard satellite-to-ground links only) and system augmented by ISL. The two systems are compared under the same hypothesis and simulated within the same software. The software is made of two distinct and independent parts : the simulation which generates the noisy pseudo-ranges, and an analysis which uses a non linear adjustment procedure in order to recover the initial parameters of the simulation and compute the quantitative error budgets. For a given application, the quantitative comparison between the error budgets of both systems allow us to highlight the relative merits of the two configurations. Our results are a further step in the characterization of the interest of ISL and should prove useful for the design of future satellite navigation system design.


  • 14 dec. 2015 (Villetaneuse) - Thesis defense of Anthony BERCY, « Ultrastable optical fiber link: multiple-users dissemination, study of fundamental and technological limits and new applications »

    Defense on Monday 14 December 2015 at 14:00 –  Amphithéâtre Euler, Université PAris 13, Villetaneuse

    Work accomplished within a collaboration between LPL and SYRTE.

    “Optical frequency links give the possibility to disseminate an ultra-stable frequency reference to many research laboratories for precise measurements as performed in frequency metrology and in applied and fundamental physics. We demonstrated first a simple branching network setup dropping an ultra-stable signal at different positions along an urban optical link of 92 km, that exhibits a relative frequency stability of 1.3×10-15 at 1 s integration time, limited by long-term diurnal thermal effects. We developed and tested an improved setup with a compact and thermalized optical interferometer and a laser diode used to feed a secon- dary link, which fiber noise is compensated. These two setup open the way to multiple-users dissemination in Paris area and on the REFIMEVE+ network.

    Second we demonstrated optical frequency comparison using a two-way method. We tested the sensitivity of this comparison over a 100 km telecommunication fiber loop network using either unidirectional or bidirectional propagation, with an excellent frequency stability thanks to the very good rejection of the fiber noise.

    These results open the way to high-resolution frequency comparison of the best optical clocks over national or international fiber networks.”

  • 09 dec. 2015 (Besançon) - Thesis defense of Irina BALAKIREVA "Non-linear dynamics of Kerr optical frequency combs"

    Defense on Wednesday december 9th, – 14:00 in Amphithéâtre Jean-Jacques Gagnepain (bât. Témis Sciences), 15B avenue des Montboucons, Besançon

    Work accomplished in FEMTO-ST under the supervision Yanne Chembo et Laurent Larger

    Thesis dedicated to the study of Kerr optical frequency combs generated in whispering gallery mode resonators.


  • 03 dec. 2015 (Nice) - Thesis defense of Liwei WEI, « High-Power Laser System for Advanced Virgo Gravitational Wave Detector: Coherently Combined Master Oscillator Fiber Power Amplifiers »

    Defense on Thursday 03 December 2015 at 10:00 – Mt Gros, Observatoire de la Côte d’Azur, Bd de l’Observatoire , Nice (salle de la Nef)

    Work accomplished in  ARTEMIS

    Virgo is a cavity-enhanced Michelson interferometer built for the direct detection of gravitational waves. The Advanced Virgo project consists of major upgrades to the Virgo gravitational wave detector for an order of magnitude improvement in differential strain sensitivity, one of which is the tenfold increase in injected laser power to 175 Watts. The use of fiber laser amplifiers and their coherent combination are foreseen to deliver the required high-power low-noise beam. In this thesis work, we review the laser requirements for gravitational wave detectors, introduce the design of the laser system for Advanced Virgo, and develop the means for laser characterization in accordance with the stringent noise specifications. We then present the results to date, notably the quasi-continuous long-term operation of two 40-Watt fiber laser amplifiers over thousands of hours and their coherent combination with Mach-Zehnder interferometry. Although the targeted power for Advanced Virgo is not yet attained, the developed system shows decent noise performance and is promising for further power-scaling efforts.

    Keywords : laser characterization, fiber laser amplifier, coherent beam combination, interferometry, gravitational wave detector


  • 27 nov. 2015 (Palaiseau) - PhD defense of Fabien THERON, “Development of a cold atom gravity gradiometer and a telecom doubled laser device for onboard applications”

    Defense on Friday 27 November 2015 at 14:00 – Institut d’Optique Graduate School (Auditorium), Palaiseau

    Work accomplished in  ONERA

    This thesis presents the development of the experimental setup allowing the measurement of two gravity gradient components and the gravity acceleration. These quantities are resulted from the measuring of rubidium cold atoms acceleration, in free fall in vacuum, by atom interferometry. For gradiometry, the differential measurement is realized between two atomic clouds spatially separated. For the measurement of vertical gradient, the use of mobile optical lattices allows to get two atom clouds from a single atomic source.

    This work presents the setting up of the complete device, in particular with the built of the vaccum chamber, laser and micro-wave systems. Lasers are based on frequency-doubled telecom technology, which allows to obtain compact and robust systems, dedicated for onboard applications. The innovative laser architecture allows to combine atom interferometry and optical lattices, while minimizing the amount of components. The laser noise has been characterized, and limits the single shot gravimetric sensitivity to 10-9 g, the single shot differential sensitivity to 10-10 g, and the single shot gradiometric sensitivity to 38 E


  • 26 nov. 2015 (Paris) - Seminar - Kurt Gibble (Penn State University, USA), « Sundry Topics on Atomic Clocks »

    Seminar on Thrusday 26 November 2015 at 11:00 – SYRTE, PAris Observatory (Salle de l’atelier)

    I’ll discuss diverse, recent work from our group. One result is our precision measurements of s-wave quantum scattering phase shifts of ultra-cold atoms in a cesium fountain. With mrad precision, we observe a series of Feshbach resonances with variations of s-wave phase shifts approaching pi. I’ll also discuss the microwave lensing frequency shift, the recent associated controversy and a connection to recoil shifts, and some unique aspects of the microwave lensing shift of PHARAO. The distributed cavity phase (1st order Doppler) shifts of PHARAO are also significantly different than those of fountains. I will discuss those as well as our plans for a Cadmium optical lattice clock.


  • 23 nov. 2015 (Orsay) - PhD defense of Alexis BONNIN : ” Dual-Species Atom Interferometry and Applications to Inertial Measurements ”

    Defense on Monday 23 November 2015 at 14:00 – Laboratoire Aimé Cotton (Salle Balmer), Orsay

    Work accomplished in  ONERA

    In the emerging issue of testing the Equivalence Principle with cold atom inertial sensors, this thesis focuses on the realization and the characterization of a simultaneous dual-species atom interferometer (87Rb & 85Rb) which allows to measure the differential acceleration in an extremely sensitive way. The Mach-Zehnder type atom interferometer relies on the simultaneous handling of atomic wave-packets with stimulated Raman transitions. The laser system is based on the frequency doubling of a single laser source at 1560 nm. All the required laser frequencies for handling both isotopes (trapping, cooling, selection, interferometry and detection) are generated by phase modulating this source. A detailed modeling of the interferometer’s inertial responses and an analysis of a method to extract the differential phase were carried out. The differential acceleration measurement led to an atom based test of the Weak Equivalence Principle of η( 87Rb, 85Rb) = (1.3 ± 3.2) × 10− 7, at the state-of-the-art. The simultaneous aspect of the experiment allowed to highlight for the first time common mode vibration noise rejection with two different atomic species, a rejection factor of 50 000 being currently achieved. The current performance of the instrument exhibits a sensitivity on the differential acceleration of 1.23 × 10− 7 g/sqrt(Hz) and a resolution of 2 × 10− 9 g for integration times lower than few hours. Finally, innovative operating modes of dual-species atom interferometers for on-board acceleration measurements are explored.


  • 20 nov. 2015 (Paris) - PhD defense of Indranil DUTTA : ” tability Improvement of a Sagnac Cold Atom Interferometer: towards Continuous Operation “

    Defense on Friday 20 November 2015 at 14:30 – Observatoire de Paris (Amphi de l’IAP), 77 avenue Denfert-Rochereau, Paris

    Work accomplished in  ONERA

    This thesis aims at pushing the performances of a cold atom interferometer principally sensitive to rates of rotation in a particular axis. In our experiment, Cesium atoms are laser cooled, trapped and launched in a fountain configuration. According to the Sagnac effect, the sensitivity of the interferometer to rotation is proportional to the area enclosed by the interferometer arms. We use stimulated Raman transitions to split the atoms in two paths and to form a folded Mach-Zehnder-like interferometer architecture using four Raman pulses. With an interrogation time of the atoms of 800 ms, we achieve a Sagnac area as high as 11 cm2. The thesis describes the improvements to the experimental setup to operate the gyroscope with such a high Sagnac area. A procedure for the relative alignment of the Raman beams at the μrad level is presented, which is critical to meet the interference condition of the cold atoms at the interferometer output. The characterization and mitigation of the vibration noise, affecting the gyroscope, is also demonstrated. We finally demonstrate a short term rotation stability of 160 nrad/s at 1 s and a long term stability of 1.8 nrad/s after 10000 s of integration time. This stability level represents a factor 5 improvement compared to the previous SYRTE gyroscope experiment of 2009 and a factor 15 compared to other published results. The thesis work also presents a new method of interrogation to operate the gyroscope without dead times, which is important for various applications of cold atom sensors in inertial navigation, geophysics and in fundamental physics.
    Keywords: Atom interferometry, cold atoms, gyroscope, Sagnac effect, stimulated Raman transitions, inertial sensor