The implementation of optical frequency standard based on direct frequency comb and Rb two-photon transitions

The authors demonstrate a method to implement optical frequency standard based on frequency comb and Rb two-photon transitions. This scheme is simple and robust, which can operate for more than two hours. It can also eliminate 95% of the Doppler-broadening background, and the fractional stability can reach 8.4×10
^-12
and 7.1×10
^-13
at 1 s and 1000 s. This frequency standard may be utilized in many applications, such as optical clock.