Drift-compensated low-noise frequency synthesis based on a CryoCSO for the KRISS-F1(Cs)

This paper reports implementation and operation of a frequency synthesizer based on a cryocooled cryogenic Sapphire oscillator (cryoCSO) for the Cesium atomic fountain clock developing at KRISS, KRISS-Fl(Cs). With use of this highly stable local oscillator, the short-term stability of KRISS-F1(Cs) was greatly improved and reaches the quantum projection noise limit, resulting in the measured lowest Allan deviation of 2.6×10
^-14
. In addition, the long-term drift (4.8×10
^-14
/day) of the cryoCSO could be compensated and reach below 5×10
^-16
/day as low as state-of-the-art active hydrogen masers.