Narrow linewidth CPT signal in small vapor cells for chip scale atomic clocks

We report our measurement of coherent-population-trapping (CPT) signal linewidths in small vapor cells, which are desirable for chip scale atomic clock (CSAC) applications. The linewidths are measured in both rubidium vapor cells and cesium vapor cells. Using a micro-machined silicon absorption cell (diameter = 1.7 mm, length = 2 mm), we demonstrate a sub-kHz linewidth (FWHM) of the clock transition in the ¹³³Cs atom (|F = 3, m_F = 0>/|F = 4, m_F = 0>). The measured intrinsic linewidths (FWHM = 777 Hz for Cs and FWHM = 1496 Hz for Rb) of the cells agree with the calculated results.