Two-Photon Spectroscopy in Rb for an Optical Frequency Standard

The Air Force Research Laboratory is pursuing optical atomic clocks for navigation and timing applications. Optical clocks are of particular interest owing to their very high oscillation frequencies. We present an optical rubidium atomic frequency standard (O-RAFS), based upon a two-photon transition at 778 nm, that utilizes readily available commercial off-the-shelf components. Compared to existing GPS clocks, O-RAFS offers reduced short-term instability ($7 \times 10^{-13}/ \sqrt{\tau}$), improved manufacturability, and competitive size, weight, and power, making it an attractive candidate for future space operation.