title: Direct frequency comb optical frequency standard based on two-photon transitions of thermal atoms.
abstract: Optical clocks have been the focus of science and technology research areas due to their capability to provide highest frequency accuracy and stability to date. Their superior frequency performance promises significant advances in the fields of fundamental research as well as practical applications including satellite-based navigation and ranging. In traditional optical clocks, ultrastable optical cavities, laser cooling and particle (atoms or a single ion) trapping techniques are employed to guarantee high stability and accuracy. However, on the other hand, they make optical clocks an entire optical tableful of equipment, and cannot work continuously for a long time; as a result, they restrict optical clocks used as very convenient and compact time-keeping clocks. In this article, we proposed, and experimentally demonstrated, a novel scheme of optical frequency standard based on comb-directly-excited atomic two-photon transitions. By taking advantage of the natural properties of the comb and two-photon transitions, this frequency standard achieves a simplified structure, high robustness as well as decent frequency stability, which promise widespread applications in various scenarios.
authors.affiliation: Department of Electronics, School of Electronics Engineering and Computer Science, Peking University, Beijing, 100871, China.
authors.forename: S Y
authors.initials: SY
authors.lastname: Zhang
authors.affiliation: Department of Electronics, School of Electronics Engineering and Computer Science, Peking University, Beijing, 100871, China.
authors.forename: J T
authors.initials: JT
authors.lastname: Wu
authors.affiliation: Department of Electronics, School of Electronics Engineering and Computer Science, Peking University, Beijing, 100871, China.
authors.forename: Y L
authors.initials: YL
authors.lastname: Zhang
authors.affiliation: Department of Electronics, School of Electronics Engineering and Computer Science, Peking University, Beijing, 100871, China.
authors.forename: J X
authors.initials: JX
authors.lastname: Leng
authors.affiliation: Department of Electronics, School of Electronics Engineering and Computer Science, Peking University, Beijing, 100871, China.
authors.forename: W P
authors.initials: WP
authors.lastname: Yang
authors.affiliation: Department of Electronics, School of Electronics Engineering and Computer Science, Peking University, Beijing, 100871, China.
authors.forename: Z G
authors.initials: ZG
authors.lastname: Zhang
authors.affiliation: Department of Electronics, School of Electronics Engineering and Computer Science, Peking University, Beijing, 100871, China.
authors.forename: J Y
authors.initials: JY
authors.lastname: Zhao