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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

Development of an optical frequency standard based upon the /sup 2/S/sub 1/2/-/sup 2/D/sub 5/2/ transition in Sr/sup +/

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

Published Jan 22, 2003• 0 citations
Publisher

Abstract

Recent work is presented on the development of an optical frequency standard, based on the /sup 2/S/sub 1/2/-/sup 2/D/sub 5/2/ transition at 674 nm in /sup 88/Sr/sup +/. Work on characterising the probe laser is also presented and the observed linewidth of one of the /spl Delta/m=0 Zeeman components of the 674 nm transition is 290 Hz. Two traps have been operated simultaneously and a null offset between them confirmed at the 3 parts in 10/sup 13/ level. The feasibility of cooling and probing /sup 87/Sr/sup +/ is also discussed.

DOI
10.1109/freq.1999.841398

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IEEE Transactions on Instrumentation and Measurement•Apr 1, 2003•10 citations
Recent work is presented on the development of an optical frequency standard, based on the /sup 2/S/sub 1/2/-/sup 2/D/sub 5/2/ transition at 674 nm in /sup 88/Sr/sup +/. Work on characterising the probe laser is also presented and the observed linewidth of one of the /spl Delta/m=0 Zeeman components of the 674 nm transition is 290 Hz. Two traps have been operated simultaneously and a null offset between them confirmed at the 3 parts in 10/sup 13/ level. The feasibility of cooling and probing /sup 87/Sr/sup +/ is also discussed.
As a key component of a strontium based optical clock, we have developed an apparatus which allows laser cooling and trapping of more than 10/sup 7/ /sup 88/Sr atoms to temperatures below 1 /spl mu/K. Using this system, we have performed the first high accuracy measurement of the /sup 88/Sr /sup 1/S/sub 0/-/sup 3/P/sub 1/ clock transition using an ultra-cold sample. Detailed descriptions of both the measurement technique and corresponding systematic uncertainties is provided. In addition, by varying the density of the ultra-cold /sup 88/Sr sample over a range of three orders of magnitude we obtain the first definitive measurement of a density-related frequency shift and linewidth broadening of an optical clock transition in an ultra-cold alkaline earth system. Spectroscopy of the /sub 1/S/sub 0/-/sup 3/P/sub 0/ transition is currently underway using this narrow probe laser and an octave spanning femtosecond laser. Our most recent results are presented. The proposed measurement technique, accuracy, and stability of an optical clock based on the EIT (electromagnetically-induced-transparency) measurement in /sup 88/Sr are described.
An optical frequency standard, based on the 674 nm 2S1/2-2D5/2 'clock' transition in a laser cooled trapped strontium ion is currently being evaluated at the UK National Physical Laboratory. The probe laser is a narrowed AlGaInP diode laser locked to a highly-stable and ultra-low- expansion high-finesse cavity. Laser linewidths of less than 200 Hz have been observed, measured by scanning over a single Zeeman component at 674 nm. The development of this laser is described, together with factors currently limiting the observed linewidth. Three 88Sr+ traps are now in operation, and the probe laser source can be simultaneously locked to the center of the 2S1/2 - 2D5/2 Zeeman multiplet in any two of the three traps, allowing a comparison between them. Recent results on this comparison are presented.
A single laser cooled ion in a radiofrequency trap can serve as the basis for a highly stable optical frequency standard. We present recent results of our work on single indium ions, using the /sup 1/S/sub 0/ to /sup 3/P/sub 0/ transition at 236.5 nm wave-length as the clock transition. This resonance has a linewidth of only 0.82 Hz where systematic shifts should be controllable on the mHz level. A single In/sup +/ ion is stored in a miniature Paul-Straubel trap and laser cooled to a temperature of about 100 /spl mu/K. The clock transition is excited using a frequency quadrupled Nd:YAG laser. A fractional resolution of 1.3/spl middot/10/sup -13/ has been achieved so far (linewidth of 170 Hz at 1267 THz). The absolute frequency of the clock transition clock transition has been measured with an uncertainty of 2/spl middot/10/sup -13/ using a frequency chain and a methane-stabilized HeNe laser as a reference, that was calibrated with a cesium clock.
We report on work directed toward the systematic evaluation of an optical frequency standard based on the /sup 2/S/sub 1/2/-/sup 2/D/sub 5/2/ transition of a single, laser-cooled, trapped /sup 199/Hg/sup +/ ion, whose resonance frequency is 1.06/spl times/10/sup 15/ Hz. For the purpose of the evaluation, a second /sup 199/Hg/sup +/ standard has been constructed. In the cooling-laser system built for the second standard, an injection-locking scheme has been applied to a CW Ti-sapphire laser. We also report optical frequency measurements of the clock transition performed over the past 21 months with the first standard. During this term, the variation of the clock transition frequency is found to be less than /spl plusmn/1/spl times/10/sup -14/.