Improving the short-term frequency stability of a magnetic-state-selected cesium beam clock with optical detection

Abstract

The microwave spectrum line shape and the signal-to-noise ratio of a compact optically detected magnetic-state-selection cesium beam clock are analyzed in this paper. As the noise analysis shows, the performance is related to the atomic utilization ratio and locking parameters when the laser frequency noise is the dominant noise source. Methods are adopted for realizing better short-term frequency stability of the clock, including using a highly efficient state-selection cesium beam tube, optimizing the locking parameters, and stabilizing the microwave power to maximize the error signal. After optimization, the signal-to-noise ratio of the clock reaches 7.0 × 103 in a bandwidth of 1 Hz and the clock demonstrates a short-term stability of 4.1 × 10−12 τ−1/2. The five-day Allan standard deviation reaches 7.7 × 10−15.

An overview of the optically detected magnetic-state-selected cesium beam clock

“…Figure 1B shows the typical Ramsey fringe of OMCC. Due to the velocity-selective effect of the state-selecting magnet, the most probable velocity of the atomic beam is slower, which results in the linewidth of the OMCC being 1.5 to 2 times narrower than that of optical pumped compact cesium clocks [28].…”

“…[17], the amplitude of the microwave field for which the error signal reaches the maximum value is not identical to that which maximize the transition probability. Thus, we demodulate the microwave frequency error signal instead to stabilize the power of the microwave field [28]. The method also minimizes the cavity pulling shift.…”

“…Noise sources are considered uncorrelated, thus the corresponding power spectrum density (PSD) can be summed directly. Reference [28] shows the detailed analysis over the SNR of the OMCC.…”

“…Atoms reach the detection zone randomly, which arousing the shot noise in the fluorescence signal [33]. The SNR corresponding to the atomic shot noise is proportional to I e /(I r + 1 2 I e ) 1/2 , where I e is the amplitude of the microwave spectrum, and I r is the fluorescent signal contributed by unwanted atoms in the detected beam because of the unideal state selection [28]. The SNR corresponding to the shot noise is proportional to the square root of the atomic flux when the ratio I r /I e is a constant.…”

“…To improve the long-term stability, the microwave power and C-field were stabilized, and the 5-days stability reached 2.7 × 10 −14 [27]. Having optimized the stabilization scheme, the design of the cesium beam tube and the laser stabilization method, we improved the frequency stability to 4.1 × 10 −12 τ −1/2 , which is better than the highperformance version of 5071A [28].…”