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Thomann, Pierre

Nom
Thomann, Pierre
Affiliation principale
Fonction
Professeur honoraire
Email
pierre.thomann@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/481

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  • Publication
    Accès libre
    An experimental study of intermodulation effects in an atomic fountain frequency standard
    (2007)
    Guéna, J.
    ;
    Dudle, Gregor
    ;
    Thomann, Pierre 
    The short-term stability of passive atomic frequency standards, especially in pulsed operation, is often limited by local oscillator noise via intermodulation effects. We present an experimental demonstration of the intermodulation effect on the frequency stability of a continuous atomic fountain clock where, under normal operating conditions, it is usually too small to observe. To achieve this, we deliberately degrade the phase stability of the microwave field interrogating the clock transition. We measure the frequency stability of the locked, commercial-grade local oscillator, for two modulation schemes of the microwave field: square-wave phase modulation and square-wave frequency modulation. We observe a degradation of the stability whose dependence with the modulation frequency reproduces the theoretical predictions for the intermodulation effect. In particular no observable degradation occurs when this frequency equals the Ramsey linewidth. Additionally we show that, without added phase noise, the frequency instability presently equal to 2 x 10-13 at 1 s, is limited by atomic shot-noise and therefore could be reduced were the atomic flux increased.
  • Publication
    Accès libre
    An electrostatic glass actuator for ultrahigh vacuum: A rotating light trap for continuous beams of laser-cooled atoms
    (2007)
    Füzesi, F.
    ;
    Jornod, A.
    ;
    Thomann, Pierre 
    ;
    Plimmer, M. D.
    ;
    Dudle, Gregor
    ;
    Moser, R.
    ;
    Sache, L.
    ;
    Bleuler, H.
    This article describes the design, characterization, and performance of an electrostatic glass actuator adapted to an ultrahigh vacuum environment (10−8 mbar). The three-phase rotary motor is used to drive a turbine that acts as a velocity-selective light trap for a slow continuous beam of laser-cooled atoms. This simple, compact, and nonmagnetic device should find applications in the realm of time and frequency metrology, as well as in other areas of atomic, molecular physics and elsewhere
  • Publication
    Accès libre
    Continuous beams of cold atoms for space applications
    (2006)
    Thomann, Pierre 
    ;
    Plimmer, M.
    ;
    Di Domenico, G.
    ;
    Castagna, N.
    ;
    Guéna, J.
    ;
    Dudle, Gregor
    ;
    Füzesi, F.
    The precision of atomic state measurements should ideally be limited by irreducible fluctuations associated with the number of atoms available, e.g. shot noise or quantum projection noise. In practice, other noise sources can limit the precision achievable; a well-known effect is the intermodulation effect, or Dick effect, which degrades the stability of atomic fountain clocks using pulsed sources. One way to beat this source of instability consists of interrogating the atoms with a microwave signal derived from exceptionally stable local oscillators, such as cryogenic oscillators, which are however bulky and not ideally suited to the constraints of space. Another way of reaching atomic-noise limited instability is to use continuous sources of cold atoms. Experimental results obtained both on a fountain standard and on an experimental Cs fountain illustrate the potential of continuous cold atomic beams for improving signal-to-noise ratio and precision of measurement. Current developments towards higher atomic beam flux are also described.
  • Publication
    Accès libre
    Theoretical study of the Dick effect in a continuously operated Ramsey resonator
    (2001)
    Joyet, Alain 
    ;
    Mileti, Gaetano 
    ;
    Dudle, Gregor
    ;
    Thomann, Pierre 
    It is well established that passive frequency standards operated in pulsed mode may suffer a degradation of their frequency stability due to the frequency (FM) noise of the Local Oscillator (LO). In continuously operated frequency standards, it has been shown that a similar degradation of the frequency stability may arise, depending on the used modulation-demodulation scheme. In this paper, we report a theoretical analysis on the possible degradations of the frequency stability of a continuous fountain due to the LO FM noise. A simple model is developed to evaluate whether or not aliasing persists. This model is based on a continuous frequency control loop of a frequency standard using a Ramsey resonator. From this model, we derive a general formula, valid for all usual modulation-demodulation schemes, for the LO frequency fluctuations due to aliasing in closed loop operation. We demonstrate that in an ideal situation and for all usual modulation waveforms, no aliasing occurs if the half-period of modulation equals the transit time of atoms in the Ramsey resonator. We also deduce that in the same conditions, square-wave phase modulation provides the strongest cancellation of the LO instabilities in closed loop operation. Finally, we show that the “Dick formula” for the specific case of the pulsed fountain can be recovered from the model by a sampling operation.
  • Publication
    Accès libre
    First results with a cold cesium continuous fountain resonator
    (2001)
    Dudle, Gregor
    ;
    Joyet, Alain 
    ;
    Berthoud, Patrick
    ;
    Mileti, Gaetano 
    ;
    Thomann, Pierre 
    We report on the design, construction, and preliminary measurements on the resonator of a continuous Cs fountain frequency standard. The construction of the resonator is described, preliminary measurements of the available atomic flux, and of the beam temperature are presented, along with the first Ramsey fringes (width ≃1 Hz) obtained in this new type of fountain. We discuss theoretical aspects of the interrogation scheme with a special view on how aliasing or intermodulation effects are suppressed in a continuous fountain.
  • Publication
    Métadonnées seulement
    An alternative cold cesium frequency standard: The continuous fountain
    (: Ieee-Inst Electrical Electronics Engineers Inc, 1999)
    Dudle, Gregor
    ;
    Mileti, Gaetano 
    ;
    Joyet, Alain 
    ;
    Fretel, Emmanuel
    ;
    Berthoud, Patrick
    ;
    Thomann, Pierre 
    We report on the primary frequency standard now under construction at the Observatoire de Neuchatel (ON). The design is based on a continuous fountain of laser-cooled cesium atoms, which combines two advantages: the negligible contribution of collisions to the inaccuracy and the absence of stability degradation caused by aliasing effects encountered in pulsed operation. The design is reviewed with special emphasis on the specific features of a continuous fountain, namely the source, the microwave cavity (TE021 mode), and the microwave modulation scheme, The possible sources of frequency biases and their expected contributions to the error budget are discussed. Based on present data, an accuracy in the low 10(-15) range and a short-term stability of 7 . 10(-14) are attainable simultaneously under the same operating conditions.
  • Publication
    Accès libre
    A continuous beam of slow, cold cesium atoms magnetically extracted from a 2D magneto-optical trap
    (1998)
    Berthoud, Patrick
    ;
    Joyet, Alain 
    ;
    Dudle, Gregor
    ;
    Sagna, N.
    ;
    Thomann, Pierre 
    Starting from a 2D magneto-optical trap where cesium atoms are permanently subjected to 3D sub-Doppler cooling and 2D magneto-optical trapping, we have produced a beam of cold atoms continuously extracted along the trap axis. The simplest extraction mechanism, presently used, is the drift velocity induced by a constant magnetic field. We have used this continuous beam of atoms to produce Ramsey fringes in a microwave cavity as a first demonstration of an atomic resonator operating continuously with laser cooled atoms. The shape of the resonance pattern allows an estimate of the axial temperature, typically 200 μK. The average velocity can be adjusted from 0.7 to 3 m/s; the trap-to-atomic-beam conversion efficiency is close to one.
  • Publication
    Accès libre
    Anisotropic magneto-optical trapping of atoms: capture efficiency and induced drift velocities
    (1996)
    Dudle, Gregor
    ;
    Sagna, N.
    ;
    Berthoud, Patrick
    ;
    Thomann, Pierre 
    An anisotropic magneto-optical trap is studied as the potential source of a continuous beam of laser-cooled atoms. Capture efficiency and cloud temperature are measured experimentally and found to be lower than in an isotropic situation with the same cooling parameters. Intensity imbalance and static magnetic field are investigated as possible extraction mechanisms. While only small drift velocities are induced by means of intensity imbalance, velocities of tens of cm s-1 are observed with a static magnetic field; the shape of the observed two-peaked velocity distributions is related to the average depth of local light-shift-induced potential wells.
  • Publication
    Accès libre
    The capture process in spherical magneto-optical traps: experiment and 1D magnetic field models
    (1995)
    Sagna, N.
    ;
    Dudle, Gregor
    ;
    Thomann, Pierre 
    The influence of the magnetic field gradient on the number of Cs atoms captured in a three-dimensional magneto-optical trap is investigated both theoretically and experimentally. Two one-dimensional models of the capture process are proposed, which differ only by the nature of the assumptions on the effect of Zeeman optical pumping. Transverse cooling beams are accounted for by a mere modification of the scattering rate. Comparison with experiment shows that the number of trapped atoms versus laser detuning, laser intensity, laser beam diameter and magnetic field gradient is best predicted by a model including all Zeeman substates of the Cs atoms. Quantitative agreement is within a factor of three in most cases of interest.