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 104 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 = 104 s, respectively.