26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Direct comb excitation for two-colour rubidium-87 optical atomic clocks

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral AIP | Atomic and Molecular Physics (ATMOP)

Description

Much of the critical infrastructure of the modern world relies on timing signals disseminated by Positioning, Navigation and Timing (PNT) networks. At the heart of these networks are portable atomic clocks, forming the essential link between high-performance laboratory clocks for testing fundamental physics and field-deployable devices for real-world applications, including aboard PNT satellites. However, there is typically a trade-off between performance and Size, Weight, Power and cost (SWaP-C).
Optical atomic clocks based on the 5S_(1/2)→5D_(5/2) two-photon transition of rubidium-87 offer a pathway for realising a low-SWaP, satellite-compatible system. Here, we investigate novel approaches to lower SWaP-C whilst maintaining competitive performance, by replacing the two conventional telecoms atomic excitation lasers with a prerequisite optical clock component, the optical frequency comb (OFC).
We demonstrate direct interrogation of the atoms with an OFC for the first time in a two-colour (776nm and 780nm) Rb clock. This scheme utilises the resonant enhancement of the nearby 5P_(3/2) intermediate state to reduce optical power requirements for driving the transition compared to the single-colour (778nm) two-photon variant, hence increasing compatibility with direct OFC interrogation. However, the introduction of multiple comb lines to the atoms can cause deleterious effects to clock performance, motivating a need for selective filtering. Further, the power per comb mode is insufficient to effectively drive the transition for an atomic clock.
Stimulated Brillouin Scattering (SBS) provides an elegant solution to both issues due to its intrinsic narrow bandwidth (tens of MHz) and high gain properties. We demonstrate SBS in a two-colour rubidium clock to selectively amplify comb modes at 1552nm and 1560nm, which are frequency-doubled for atomic interrogation. We demonstrate spectroscopy using different SBS gain media, with stability measurements comparing clock performance between the two schemes.