A transportable calcium atomic beam optical clock

Achievement on atomic optical clock, which has reached to 10^-18 level uncertainty, accelerates the research of the fundamental physics. But enormous volume size limits the application of optical clock outside the lab. Here, we report a transportable Calcium atomic beam optical clock with higher stability than general microwave clocks. In this system, we use the electron-shelving method to greatly improve the signal-to-noise of 657 nm signal. After locking, the stability of transportable Calcium atomic beam optical clock is 3.0 × 10^-14 at 1 s and decreases to 2.9 × 10^-15 at 200 s with continuous working time 11000 s by self-evaluation. Then we have used a 750 MHz repetition frequency optical frequency comb to transfer Calcium atomic beam optical clock frequency to microwave and compare with Hydrogen maser. The frequency stability of Calcium atomic beam optical clock versus hydrogen maser reaches to 1.62 × 10^-12 at 1 s, which is close to the frequency stability of Hydrogen maser. The whole system is specially designed for robustness. Besides, a new full-sealed Calcium atomic beam vacuum system without flanges is constructed.