A compact optical clock scheme based on caesium atomic beam

We report a compact optical clock scheme based on caesium (Cs) atomic beam, which extends the application of Cs from microwave frequency standard to optical frequency standard. Considering the 1.2 MHz narrow natural-linewidth of the excited state 7P1/2 and 7P3/2, we can lock the laser frequency on the 455 nm or 459 nm transition line with the method of saturated absorption spectroscopy (SAS) to achieve a compact optical clock. Under the condition of 1.4 MHz narrow-linewidth laser spectrum and 100,000 signal to noise ratio (SNR), the limited stability of the compact Cs optical clock is expected to be 2.2×10-14 at 1 s. The performance of this Cs optical clock is superior to that of hydrogen atomic clock. Compared with the traditional Cs atomic clocks, the compact Cs optical clock has potentially better stability.