Development of Cs atomic fountain frequency standard at CRL

Communications research laboratory (CRL) has been developing a Cesium atomic fountain primary frequency standard. Cs atoms are cooled to below 2 μK by both magneto-optical trap (MOT) and polarization gradient cooling (PGC), and launched vertically by moving molasses method. The launched atoms pass through a microwave cavity twice, on the way upward and downward, and give rise to Ramsey resonance. We succeeded to observe narrower than 1Hz Ramsey signal, and tried to lock the microwave frequency to the atomic resonance. This report presents the current status of the development of CRL atomic fountain.