Improvement of Laser Frequency Stabilization for the Optical Pumping Cesium Beam Standard

A method is presented to improve the laser frequency stabilization for the optical pumping cesium clock. By comparing the laser frequency stabilization of different schemes, we verify that the light angle is an important factor that limits the long-term frequency stability. We minimize the drift of the light angle by using a fiber-coupled output, and lock the frequency of a distributed-feedback diode laser to the fluorescence spectrum of the atomic beam. The measured frequency stability is about 3.5 ×10^?11 at 1 s and reaches 1.5 ×10^?12 at 2000 s. The Allan variance keeps going down for up to thousands of seconds, indicating that the medium- and long-term stability of the laser frequency is significantly improved and perfectly fulfills the requirement for the optical pumping cesium clock.