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Physica Scripta

Single Trapped Ions for Optical Frequency Standards

Hugh A. Klein, G. P. Barwood, Patrick Robert Gill, Guozheng Huang

Published Jan 1, 2000• 6 citations
Publisher

Abstract

A number of laboratories are working towards developing optical frequency standards based on single trapped ions. The options are briefly reviewed. Recent progress using the singly ionised strontium system at the National Physical Laboratory (NPL) is outlined. A comparison of the frequency of the 2 S 1/2 – 2 D 5/2 transition at 674 nm in 88 Sr + , observed simultaneously in two traps, showed agreement at the 3 parts in 10 13 level. The possibility of cooling and probing 87 Sr + has recently been proposed because it offers a 674 nm transition between m F = 0 levels which is independent of magnetic field to first order. Trapping of 87 Sr + ions prepared using an oven containing an isotopically enriched strontium compound has been demonstrated at NPL.

DOI
10.1238/physica.topical.086a00033

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Apr 30, 1993•8 citations
A number of laboratories are working towards developing optical frequency standards based on single trapped ions. The options are briefly reviewed. Recent progress using the singly ionised strontium system at the National Physical Laboratory (NPL) is outlined. A comparison of the frequency of the 2 S 1/2 – 2 D 5/2 transition at 674 nm in 88 Sr + , observed simultaneously in two traps, showed agreement at the 3 parts in 10 13 level. The possibility of cooling and probing 87 Sr + has recently been proposed because it offers a 674 nm transition between m F = 0 levels which is independent of magnetic field to first order. Trapping of 87 Sr + ions prepared using an oven containing an isotopically enriched strontium compound has been demonstrated at NPL.
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Two 674-nm optical frequency standards based on the2S1/2-2D5/2transition in88Sr+are under development at NPL. Comparison of the standards allows determination of the frequency stability and reproducibility via difference frequency measurements. A relative frequency stability between the traps of ap3times10-15over a 100 s averaging time has been observed. A compact, transportable system is also being developed, which could find application in ground stations or as an optical frequency clock in space.
We describe the recent advances of the NRC single ion based optical frequency standard using the 445-THz S-D transition in88Sr+. Laser cooled confinement and probing of the clock transition has been obtained for periods exceeding 24 hours showing high levels of stability. Spectral resolutions better than 5 Hz at 445 THz have been obtained. Work is described on the development of an improved ion trap system and the continuous linkage of the optical frequency to the RF domain using a fiber based frequency comb.
The development of an all-solid-state systems of lasers is described for the cooling and probing of strontium ions in a radio-frequency (rf) trap. The Sr+ ions created within the rf trap are laser cooled by repeated cycling on the 422 nm 2S1/2 - 2P1/2 resonance transition. The 422 nm light was generated from a single mode 70 mW 844 nm diode laser, whose output was frequency doubled to 422 nm in a KNbO3 crystal inside a resonant enhancement cavity. Decays from the Sr+ upper resonance level into the 2D3/2 metastable state remove ions from the cooling cycle. This loss was prevented by driving the 1092 nm 2D3/2 - 2P1/2 transition using a Nd3+-doped fiber laser, diode-pumped at 826 nm. The 2S1/2 - 2D5/2 optical 'clock' transition at 674 nm has a natural linewidth of 0.4 Hz and may be probed with an AlGaInP laser diode. The laser diodes at 844 nm and 674 nm are both collimated using a piezo-mounted GRIN rod which also provides longitudinal mode selection. The spectral output is optically narrowed using resonant optical feedback.