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 (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.

An extended-cavity diode laser at 852 nm has been built especially for the purpose of cooling and probing cesium atoms. It is a compact, self-aligned, and continuously tunable laser source having a 100-kHz linewidth and 60-mW output power. The electronic control of the laser frequency by the piezodriven external reflector covers a 4.5-kHz bandwidth, allowing full compensation of acoustic frequency noise without any adverse effect on the laser intensity noise. We locked this laser to Doppler-free resonances on the cesium D(2) line by using the Zeeman modulation technique, resulting in the frequency and the intensity of the laser beam being unmodulated. We also tuned the locked laser frequency over a span of 120 MHz by using the dc Zeeman effect to shift the F = 4-F' = 5 reference transition.

To achieve a primary frequency standard based on a continuous fountain of laser cooled cesium atoms, we report on the production of a bright, slow and cold continuous atomic beam. Atoms are cooled from a thermal vapor in a 45° laser geometry and launched directly from the optical molasses by the moving molasses technique. The effects of the source fluorescence on the continuous beam (average velocity, temperature and flux) have been observed, and ways to optimize simultaneously the atomic capture and the continuous beam are presented. Flux measurements rise to 2×108 at/s from a 2D magneto-optical trap at 7 m/s. The initial velocity is easily tunable from 1 to 10 m/s. If the longitudinal temperature is about 70 μK, additional transverse cooling even reduces the transverse temperature in one dimension below 30 μK. By extrapolating the obtained atomic flux to the continuous fountain under construction, we expect a short-term stability of 7×10-14τ-1/2. Other applications of continuous beams of cold atoms are suggested

A primary frequency standard based on a continuous fountain of laser cooled cesium atoms is investigated. Results on a feasibility experiment demonstrate the ability of the moving molasses technique to extract a sufficiently intense cold continuous atomic beam. A general overview of such a device and its main parts is described. Stability and accuracy issues are discussed.

By the moving molasses technique we have extracted laser-cooled cesium atoms in a continuous way directly from an optical molasses. The mean launching velocity is precisely tunable from 1 to 12 m/s. The atomic beam has a flux of 1.3 x 10(8) atom/s at 7 m/s and a longitudinal temperature of 70 mu K; which represents the highest flux and lowest velocity spread obtained so far in a continuous beam of cold atoms. These features makes it well suited for atomic fountains. The atomic flux can be slightly increased in a two-dimensional magneto-optical trap operation (+40%). A simple model accounts for the observed dependence of the flux with the magnetic-field gradient. [S1050-2947(99)51212-2].

We have performed numerical simulations for three atomic clocks using cold cesium atoms

Two photon spectroscopy in rubidium is a promising tool in order to build an optical standard around 778 nm. The paper presents an experiment attempting to observe the two photon 5S-5D transition in /sup 85/Rb atoms in a magneto-optical trap.

Frequency-doubled diode-laser pumped Nd:YAG laser can constitute an interesting optical standard around 532nm. More than ten of I-127(2) lines can be observed inside the laser spectral range. Two independent systems, stabilized on one I-127(2) hyperfine component, are used to check the frequency long term stability for metrological purpose.

No lasing on other wavelengths than basic transition (A = 2.79 pm) for YSGG:Cr:Er was observed in the resonator without dispersive element. For output mirrors we used dielectric ones with variable reflectivity in the range of 2.6-2.9 pm as well as plane parallel Ge and Si plate with constant reflectivity R = 0.8 and 0.7, respectively, for all wavelengths. Using Ge prism, lasing at 16 lines was observed. Laser wavelengths corresponded to transitions between almost all sublevels of 41,,,1-41,3,2 multiplet. The best laser output was achieved by using lithium niobate prism. Using LiNbO, prism as electro-optical modulator, Q-switch operation was obtained with tuning over 4 lines with energy up to 5 mJ in TEM, mode.

Frequency-doubled diode-laser-pumped Nd:YAG laser can constitute an interesting optical standard around 532 nm. More than ten of /sup 127/I/sub 2/ lines can be observed inside the laser spectral range. Two independent systems, stabilized on one /sup 127/I/sub 2/ hyperfine component, are used to check the frequency long term stability for metrological purpose.<>