Operation of NIM5 fountain with 1.5x10^-15uncertainty and design of new NIM6 in NIM

Abstract

Abstract. The cesium fountain primary frequency standard NIM5 started to operate since 2008 and started to report to BIPM since 2014. The major constrains of NIM5 is a relatively large background signal at the detection and microwave leakages due to the Ramsey cavity. A new fountain clock NIM6 is under construction. Besides some improvements on the vacuum system, a new Ramsey cavity and a microwave synthesizer are made to reduce the Type B uncertainty. Another feature of NIM6 is collecting atoms from a MOT loading optical molasses to get more atoms with a more uniform density distribution. With a new frequency synthesizer based on cryogenic sapphire oscillator (CSO), NIM6 is aiming to reach the quantum projection noise, thus leading to a reduced Type A uncertainty compared with NIM5.

Integrated, reliable laser system for an 87Rb cold atom fountain clock

“…Consequently, our laser system is more compact than previous schemes and mechanically reliable. [2][3][4][5][6][7][8][9][10][11][12][13][13][14][15][16][17][18][19][20][21][22]…”

“…[8] A reliable fountain clock with more portability would be very helpful for time keeping and time services. [9][10][11][12] In a previously developed fountain clock system, we integrated commercial lasers, laser amplifiers, frequency shifting components and laser beam splitter components into an optical table to create a transportable rubidium fountain clock. Long-term tests of the fountain clock were conducted in Shanghai and Beijing, with performance being similar in the two cities.…”