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Conference on Precision Electromagnetic Measurements

Development of an indium ion optical frequency standard

Ying Li, Nozomi Ohtsubo, Kensuke Matsubara, Shigeo Nagano, Kazuhiro Hayasaka

Published Aug 1, 2014• 0 citations
Publisher

Abstract

We report on the progress toward an indium ion optical frequency standard with an expected accuracy of 10-18. A115In+has been successfully prepared by sympathetic cooling with two laser-cooled40Ca+ions. The clock laser at 237 nm has been constructed as the forth harmonic of an amplified diode laser with a linewidth smaller than 0.9 Hz. After beam shaping and intensity stabilization a power over 10 mW is available for the clock transition (1S0-3P0) interrogation. Observation of the clock transition is in progress by employing the electron shelving method using the1S0-3P1transition at 230 nm.

DOI
10.1109/cpem.2014.6898258

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Conference on Precision Electromagnetic Measurements•Jul 1, 2016•0 citations
We report on the progress toward an indium ion optical frequency standard with an expected accuracy of 10-18. A115In+has been successfully prepared by sympathetic cooling with two laser-cooled40Ca+ions. The clock laser at 237 nm has been constructed as the forth harmonic of an amplified diode laser with a linewidth smaller than 0.9 Hz. After beam shaping and intensity stabilization a power over 10 mW is available for the clock transition (1S0-3P0) interrogation. Observation of the clock transition is in progress by employing the electron shelving method using the1S0-3P1transition at 230 nm.
We report on the current status of the optical frequency standard based on a single 115In+ ion. A single Indium ion is being trapped in a Paul-Strauble type trap and cooled in combination of Doppler cooling and sideband cooling to its lowest vibrational states. To interrogate the1S0-3P0clock transition with high accuracy we demonstrate a Hz-level laser system resonant to this transition. With the current setup we are able to achieve a measured linewidth of the clock transition of 260 Hz. The statistical uncertainty of the absolute frequency measurement is 3×10-13, limited mainly by our reference frequency standard.
Single laser-cooled ions in radiofrequency traps can serve as the basis for highly stable optical frequency standards. Here we present recent results on In+, using the 1S0 yields 3P0 line at 236.5 nm wavelength as the clock transition. This resonance has a natural linewidth of only 0.82 Hz and systematic shifts should be controllable at the mHz level. A single indium ion is stored in a miniature Paul- Straubel trap and laser cooled to a temperature of about 100 (mu) K. The clock transition is excited using a frequency quadrupled 946 nm Nd:YAG laser. A fractional resolution of 1.3 (DOT) 10-13 has been achieved so far (linewidth of 170 Hz at 1267 THz). The absolute optical frequency of the clock transition has been measured with an uncertainty being less than 3 (DOT) 10-13 using a frequency chain and a methane-stabilized HeNe laser that was calibrated with a cesium clock.
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.
A single laser-cooled indium ion is a promising candidate for an ultimate resolution optical time or frequency standard. It can be shown that single ions from group IIIA of the periodic table (indium, thallium, etc.) can have extremely small systematic errors. In addition to being free from Doppler, transit-time and collisional shifts, these ions are also quite insensitive to perturbations from ambient magnetic and electric fields (mainly due to the use of a J=0-0 transition for spectroscopy). Of all group IIIA ions, indium seems to be the most practical, since it is heavy enough to have a tolerable intercombination cooling transition rate and (unlike thallium) has transitions which are easily accessible with frequency multiplied continuous-wave lasers. A single indium ion standard has a potential inaccuracy of one part in 10(exp 18) for integration times of 10(exp 6) seconds. We have made substantial progress during the grant period in constructing a frequency standard based upon a single indium ion. At the beginning of the grant period, single indium ions were being successfully trapped, but the lasers and optical systems were inadequate to achieve the desired goal. We have considerably improved the stability of the dye laser used to cool the ions and locked it to a molecular resonance line, making it possible to observe stable cooling-line fluorescence from a single indium ion for reasonable periods of time, as required by the demands of precision spectroscopy. We have substantially improved the single-ion fluorescence signal with significant benefits for the detection efficiency of forbidden transitions using the 'shelving' technique. Finally, we have constructed a compact, efficient UV 'clock' laser and observed 'clock' transitions in single indium ions using this laser system. We will elaborate on these accomplishments.