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.