In this paper we report our design and experimental results towards demonstration of a magneto optical trap (MOT)-based cold Cs-beam atomic clock. We generated a continuous cold Cs beam from a Cs MOT by perturbing the MOT potential and measured the longitudinal velocity of the Cs beam to be 7 m/s. In order to separate the atomic beam from the MOT laser beam, we used a onedimensional optical molasses to deflect the Cs beam through an angle of 30 o before the atomic beam enters the microwave cavity. Our Cs beam has an instantaneous atomic flux of 3.6 × 10 10 atoms/s when operated in pulsed mode and a continuous flux of 2 × 10 8 atoms/s. Under current experimental conditions, the observed cold Cs atomic beam parameters infer a shortterm, shot-noise limited Allan standard deviation of 2.7 × 10 -13 τ -1/2 (τ is the averaging time) for the cold Cs beam clock under development.

Although atomic clocks have very low levels of frequency instability, they are nonetheless sensitive (albeit slightly) to various environmental parameters, including temperature, power supply voltage, and dc magnetic fields. In the terrestrial environment, however, atmospheric pressure (i.e., the air's molecular density) is not generally included in this list, because the air's density variations near the surface of the earth will typically have a negligible effect on the clock's performance. The situation is different, however, for clocks onboard satellites like Galileo, where manufacturing and testing are done at atmospheric pressure, while operation is in vacuum. The pressure sensitivity of atomic clocks, in particular vapor-cell atomic clocks, can therefore be of significance. Here, we discuss some of the ways in which changes in atmospheric pressure affect vapor-cell atomic clocks, and we demonstrate that, for one device, the pressure-sensitivity traces back to a pressure-induced change in the temperature of the clock's filter and resonance cells.

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