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Joyet, Alain

Nom
Joyet, Alain
Affiliation principale
Fonction
Post-doctorant
Identifiants
https://libra.unine.ch/handle/123456789/482

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  • Publication
    Accès libre
    Theoretical analysis of aliasing noises in cold atom Mach-Zehnder interferometers
    (2012)
    Joyet, Alain 
    ;
    Di Domenico, Gianni 
    ;
    Thomann, Pierre 
    We present a theoretical analysis of aliasing noises that might appear in cold atom Mach-Zehnder interferometers used for the measurement of various physical quantities. We focus more specifically on single cold atom gyroscopes. To evaluate the level of aliasing noises, we have developed a model based on the power spectral densities of the different identified noise sources as input parameters and which makes use of a servo-loop to realize a precise measurement of the rotation rate. The model allows one to take into account different modes of operation, like a continuous as well as a pulsed or even a multi-ball operation. For monokinetic atoms, we show that the intermodulation noise can be completely filtered out with a continuous mode of operation and an optimum modulation scheme for any modulation frequency but also with a pulsed operation however only for specific launching frequencies. In the case of a real continuous atomic beam having a velocity distribution, it comes out that a high attenuation can be reached which indicates clearly the potential stability improvement that can be expected from a continuous operation.
  • Publication
    Accès libre
    Improvement of the frequency stability below the dick limit with a continuous atomic fountain clock
    (2012)
    Devenoges, Laurent 
    ;
    Stefanov, A.
    ;
    Joyet, Alain 
    ;
    Thomann, Pierre 
    ;
    Di Domenico, Gianni 
    The frequency instability of a shot-noise limited atomic fountain clock is inversely proportional to its signal-to- noise ratio. Therefore, increasing the atomic flux is a direct way to improve the stability. Nevertheless, in pulsed operation, the local oscillator noise limits the performance via the Dick effect. We experimentally demonstrate here that a continuous atomic fountain allows one to overcome this limitation. In this work, we take advantage of two-laser optical pumping on a cold cesium beam to increase the useful fountain flux and, thus, to reduce the frequency instability below the Dick limit. A stabil- ity of 6 • 10-14 τ-1/2 has been measured with the continuous cesium fountain FOCS-2.
  • 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
    Accès libre
    An alternative cold cesium frequency standard: the continuous fountain
    (2000)
    Dudle, G.
    ;
    Mileti, Gaetano 
    ;
    Joyet, Alain 
    ;
    Fretel, Emmanuel
    ;
    Berthoud, P.
    ;
    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.