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

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 or 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 percent 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.