Broadband, unpolarized repumping and clearout light sources for Sr$^+$ single-ion clocks

TL;DR

This paper presents compact, broadband, unpolarized light sources for Sr+ single-ion optical clocks that are easy to use, do not require stabilization, and demonstrate high efficiency and low temperature operation.

Contribution

It introduces fiber-based, inexpensive, and stable broadband light sources for Sr+ clocks that eliminate the need for frequency stabilization and external modulators.

Findings

Achieved 100% clearout efficiency in tests with a single-ion standard.

Demonstrated near-Doppler-limit ion temperatures of 1-1.5 mK.

Showed potential for similar sources for Ca+ and Ba+ ions.

Abstract

Future transportable optical clocks require compact and reliable light sources. Here, broadband, unpolarized repumper and state clearout sources for Sr+ single-ion optical clocks are reported. These turn-key devices require no frequency stabilization nor external modulators. They are fiber based, inexpensive, and compact. Key characteristics for clock operation are presented, including optical spectra, induced light shifts and required extinction ratios. Tests with an operating single-ion standard show a clearout efficiency of 100%. Compared to a laser-based repumper, the achievable fluorescence rates for ion detection are a few tens of per cent lower. The resulting ion kinetic temperature is 1--1.5 mK, near the Doppler limit of the ion system. Similar repumper light sources could be made for Ca+ (866 nm) and Ba+ (650 nm) using semiconductor gain media.