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PACS. 32.80Pj -Optical cooling of atoms; trapping. PACS. 42.50Vk -Mechanical effects of light on atoms, molecules, electrons, and ions.Abstract. -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 mK. The average velocity can be adjusted from 0.7 to 3 m/s; the trap-to-atomic-beam conversion efficiency is close to one.

Abstract-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.Index Terms-Atomic fountain, atomic frequency standards, Dick effect.

Abstract-We report on the primary frequency standard now under construction at the Observatoire de Neuchâtel (ON). The design is based on a continuous fountain of lasercooled 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 (TE 021 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.