Improving the Medium-long Term Frequency Stability of Pulsed Optically Pumped Rubidium Clock

In this paper, we present the improvements of the medium-long term frequency stability of the POP atomic clock. A new temperature servo system with higher temperature stability is developed. The temperature fluctuation of the cavity is 27 μK at 10
⁴
s, which is improved by approximately one order of magnitude compared to previous result. And the whole physics package is sealed inside a vacuum chamber. With these improvements, the frequency stability of 2.2 × 10
^-13
and 7.8 × 10
^-15
are achieved at an average time of τ = 1 s and τ = 10
⁴
s, respectively.