The atomic fountain operation is sequential (cycle duration 1 - 1,6 s). At each cycle, a few 106 up to 107 atoms are captured in an optical molasses, at the intersection of six laser beams, then cooled down to a temperature of the order of one µK, from an atomic vapour or a slow beam issued from a two dimensional magneto-optical trap. Then launched vertically inside the vacuum chamber at a velocity of a few m/s, they perform a ballistic flight up to an apogee of the order of 1 m, before (...)
SYRTE is the pioneering laboratory in the development of atomic fountains. The first clock based on this type of device is operating since 1993. Atomic fountains take full benefit of atom laser cooling techniques, which enables a gain in performances by several orders of magnitude compared to conventional clocks based on thermal beams: their relative frequency stability reaches a few 10-14 at one second and their accuracy a few 10-16.
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Principle of operation
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Frequency stability and accuracy
Since 1967, the second of the international system of units is defined from the resonance of the cesium 133 atom corresponding to the transition between the two hyperfine levels |F = 3> and |F = 4> of the electronic state 6S1/2. The frequency of this transition has been fixed to the conventional value ν0 = 9 192 631 770 Hz, for an isolated atom.
The performances of clocks are characterized by their frequency stability and frequency accuracy : stability is the capacity of the device to (...) -
The atomic fountain ensemble at SYRTE
Three atomic fountains are operational at SYRTE:
FO1 which has been the first 133Cs fountain to be constructed and exploited in time-frequency metrology. Its vacuum chamber is equipped with test tools dedicated to measurement of the Stark effect or of the blackbody radiation shift, and it has also been exploited to qualify the space clock PHARAO.
FO2 is a dual fountain, unique in the world, operating simultaneously with 133Cs and 87Rb atoms. FO2 has demonstrated the record of stability (...) -
Applications of atomic fountains
Contributions to international timescales The first application of atomic fountain is to realize the second of the international system of units. It is the BIPM (International Bureau for Weights and Measures) which is in charge of centralizing the data of the contributing laboratories and of calculating the international timescales: UTC (Coordinated Universal Time) and TAI (International Atomic Time), as well as the second of the SI. Currently, over the twenty or so atomic fountains under (...)
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Applications des fontaines atomiques
Contributions aux échelles de temps internationales La première application des fontaines atomiques est de réaliser la seconde du Système d’unités International (SI). C’est le BIPM (Bureau International des Poids et Mesures), qui est en charge de centraliser les données des laboratoires contributeurs et de calculer les échelles de temps internationales : UTC (Temps Universel Coordonné) et TAI (Temps Atomique International), ainsi que la seconde du SI. Actuellement, sur la vingtaine de fontaines (...)