Compact cesium atomic fountain clock

For most of the cesium fountain clocks, the microwave cavities together with the cesium atoms are enclosed in a huge vacuum chamber. In our new design, the microwave cavity is not in the vacuum chamber. A fused quartz tube is inserted through a cylindrical cavity via two 10-mm-diameter-holes at the end caps of the cavity. In such a configuration, the vacuum feed-through for the wave-guide is not necessary, and the size of the vacuum chamber can be obviously reduced. Some perturbations of the microwave cavity including cavity quality factor and resonant frequency from inserting in the quartz tube are estimated. It seems that the quartz tube does not cause serious problems.