Short-term stability of a microcell optical reference based on Rb atom two-photon transition at 778 nm

TL;DR

This paper demonstrates a microcell-based rubidium two-photon transition optical frequency reference with promising short-term stability, suitable for miniaturized high-stability clocks in navigation, communications, and metrology.

Contribution

It introduces a microfabricated vapor cell optical frequency reference based on rubidium two-photon transition and characterizes its short-term stability, showing potential for compact high-precision clocks.

Findings

Short-term stability of 3.5×10^{-13} τ^{-1/2} up to 200 s

Phase noise level of +43 dBrad^2/Hz at 1 Hz offset

Photon shot noise and laser frequency noise are main stability limits

Abstract

We report on the development and short-term stability characterization of an optical frequency reference based on the spectroscopy of the rubidium two-photon transition at 778 nm in a microfabricated vapor cell. When compared against a 778 nm reference signal extracted from a frequency-doubled cavity-stabilized telecom laser, the short-term stability of the microcell frequency standard is 3.5 $\times$ 10$^{-13}$ $\tau^{-1/2}$ until 200~s, in good agreement with a phase noise level of $+$ 43 dBrad$^2$/Hz at 1~Hz offset frequency. The two main contributions to the short-term stability of the microcell reference are currently the photon shot noise and the intermodulation effect induced by the laser frequency noise. With still a relevant margin of progress, these results show the interest of this spectroscopic approach for the demonstration of high-stability miniaturized optical vapor cell clocks. Such clocks are poised to be highly beneficial for applications in navigation, communications, and metrology.