Compact optically pumped cesium beam atomic clock with a 5-day frequency stability of 7×10-15.

Compared to other commercial atomic clocks in the time keeping field, the greatest advantage of cesium beam atomic clocks is their superior long-term stability. Compared to magnetic state-selection clocks, optically pumped cesium beam atomic clocks have more interacting atoms, which results in better stability potential. To achieve good long-term stability, we propose methods including stabilization of laser power and reconstruction of circuits. They play a key role in the long-term stability of cesium beam atomic clocks. After 75 days of continuous running and measurement, we released the 5-day stability results (7×10-15 Allan deviation) of our optically pumped cesium beam atomic clock. To the best of our knowledge, this is the best 5-day stability result ever reported for compact optically pumped cesium beam atomic clocks.

A linewidth locking method to control the microwave power in optically pumped cesium-beam clocks.

In this paper, we present a linewidth locking method to control the microwave power in optically pumped cesium-beam frequency standards. The responses of optically pumped cesium-beam tubes and classical cesium-beam tubes are analyzed and compared against the power of the microwave field. Due to the wide probability distribution of atomic velocity resulting from the optical state preparation and detection, the linewidth of the Ramsey pattern is sensitive to the microwave power. The results can be used to control the microwave power instead of using the traditional extremum method. The advantages of the new method are discussed, and we named this new method the linewidth locking method. When the microwave power is well controlled at a low level by the linewidth locking method, the frequency stability of cesium-beam clocks will be improved to a certain degree for the reduction of the Ramsey pattern linewidth. In experiment, using the linewidth locking method, the Allan deviation of our optically pumped cesium-beam frequency standard is 2.64×10-12/τ and continues until the averaging time exceeds 1 × 105 s, which is 17% better than that using the traditional extremum method.

Frequency instability of a miniature optically pumped cesium-beam atomic frequency standard.

This paper proposes a miniature optically pumped cesium-beam atomic frequency standard with a volume of 38.4 l and a weight of 28 kg and examines the main factors that affect its signal-to-noise ratio (SNR). Methods to improve the SNR are proposed, which improve the short-term frequency instability: installing a collimator at the exit of the cesium oven, using the beam fluorescence spectrum with the fiber-coupled output to stabilize the laser frequency, and using the 4-5 cycling transition of the cesium D2 line for the atomic detection. We also examine several frequency shifts that affect the long-term frequency instability and detail methods to reduce these shifts. At present, the frequency instability achieved by the Peking University miniature optically pumped cesium-beam frequency standard has reached 3.12×10-12/τ.