Residual frequency drift in an atomic fountain clock

Abstract

We report a locking mode in which the local oscillator (LO) is locked to an atomic fountain and calibration of the residual frequency drift (RFD). In this running mode, the locked LO outputs a standard frequency signal, and a short-term fractional frequency stability of 2.7 \times 10-13τ-1/2 is achieved. Due to the frequency drift of the LO in free running mode, a systematic frequency bias, or RFD, exists after being locked by the atomic fountain. We analyze and measure the RFD with a value of -3(2) \times 10-16. A sectionalized post-process method is adopted to calibrate the RFD.