Preliminary Results of Active Optical Clock with Cavity-Length Stabilization

Abstract

We have experimentally demonstrated the active optical clock with a good suppression to cavity-length noise compared with the passive one. However, the frequency stability of the four-level active optical clock for thermal atoms is still limited by the residual cavity-pulling effect. In this paper, we preliminarily realized the cavity-length stabilization in 1064/1470 nm dual-wavelength good-bad cavity system. The synchronous cavity-length change between two dual-wavelength systems is realized by using the phase locking technique of 1064 nm good-cavity lasers. Therefore, the beating linewidth of 1470 nm bad-cavity lasers will also be reduced considering that the 1064/1470 nm dual-wavelength lasers share the one cavity. The tracking accuracy of 1064 nm good-cavity lasers is better than $3 \times 10^{-16}$ at 1s after phase-locking, and the linewidth of 1470 nm bad-cavity laser is reduced to 77 Hz. The linewidth of active optical frequency standard is still limited by the light shift, collision shift and Zeeman shift. The beating signal of magnetic sublevels corresponding to the Cs 1470 nm clock transition is observed under Zeeman effect. Further research is needed, such as, the design of vacuum chamber and magnetic shielding, to reduce the linewidth of the continuous 1470 nm active optical frequency standard.