Shelving spectroscopy of the strontium intercombination line

TL;DR

This paper demonstrates a shelving spectroscopy method for the narrow 689-nm intercombination line of strontium, enhancing signal detection in atomic beams and vapor cells, with potential applications in low-complexity optical clocks.

Contribution

It introduces a robust shelving detection scheme for strontium spectroscopy that improves signal strength and can be easily implemented in existing experimental setups.

Findings

Achieved fractional frequency instability of ~2×10⁻¹² at 1 s

Demonstrated spectroscopy in atomic beams and vapor cells

Enhanced signal detection compared to direct fluorescence

Abstract

We present a spectroscopy scheme for the 7-kHz-wide 689-nm intercombination line of strontium. We rely on shelving detection, where electrons are first excited to a metastable state by the spectroscopy laser before their state is probed using the broad transition at 461 nm. As in the similar setting of calcium beam clocks, this enhances dramatically the signal strength as compared to direct saturated fluorescence or absorption spectroscopy of the narrow line. We implement shelving spectroscopy both in directed atomic beams and hot vapor cells with isotropic atomic velocities. We measure a fractional frequency instability $\sim 2 \times 10^{-12}$ at 1 s limited by technical noise - about one order of magnitude above shot noise limitations for our experimental parameters. Our work illustrates the robustness and flexibility of a scheme that can be very easily implemented in the reference cells or ovens of most existing strontium experiments, and may find applications for low-complexity clocks.