TOWARDS DEMONSTRATION OF A MOT-BASED CONTINUOUS COLD CS-BEAM ATOMIC CLOCK

摘要

Laser-cooled low-velocity (v < 10 m/s) atomic beams have been considered to be feasible cold atom sources in developing compact and highly stable atomic clocks for satellite applications. A cold atomic beam can be realized by laser-accelerating an ensemble of ultra-cold (T <1 mK) atoms from a laser-cooled magneto-optical trap (MOT). This technique has the unique advantage of generating a useful cold atomic beam just outside the volume of a MOT and, hence, can greatly reduce the size of the atomic clock physics package. In this paper, we present our design and experimental results towards demonstration of a MOT-based cold Cs-beam atomic clock. We have generated a continuous cold Cs beam from a Cs MOT and have determined the typical longitudinal velocity of the Cs beam by Time of Flight (TOF) method to be 7 m/s with a velocity spread of 1 m/s. By adjusting the MOT parameters, the atomic beam velocity can be tuned continuously, with the velocity spread remaining to be 1 m/s. In order to separate the atomic beam from the MOT laser beam, we have used a one-dimensional optical molasses to efficiently deflect the cold Cs beam through an angle of 30 degrees. The 1-D optical molasses is set up in such a way that the molasses laser beams are perpendicular to the final atomic beam propagation path. Thus, the Cs-beam velocity components along the molasses axis are efficiently damped to nearly zero, while the Cs velocity component along the final atomic beam propagation path is unaffected. Our simulation indicates that a deflection efficiency of 100% is achievable for MOT-based cold atomic beams. Our cold Cs beam has an instantaneous atomic flux of 3.6 ×10~(10) atoms/s when operated in pulsed mode and an estimated continuous beam flux of 2 × 10~8 atoms/s. With a compact Ramsey cavity of 13 cm in length, we have estimated a short-term, shot-noise limited Allan standard deviation of 2.7 × 10~(-13) τ~(1/2)(τ is the averaging time) for the atomic clock in this work. Experiments of generating Ramsey interference fringes using the deflected, "dark" cold Cs atomic beam are in progress.