Abstract

We have developed an optical frequency standard at 445 THz (674 nm), based on the 5s ²S_1/2−4d²D_5/2 transition in a single trapped ⁸⁸Sr⁺ ion. The ion is held in a miniature RF Paul trap and its spectrum is probed by an ultra-stable diode laser system. In a series of measurements performed in 1997 and 1998, a Cs-based frequency chain was used to measure the centre frequency of the Zeeman component resolved, Sr⁺ S-D spectrum. A value of f_SD=444 779 044 095.4 kHz with an uncertainty of ±0.2 kHz (5×10⁻¹³) was determined. The magnitudes of the systematic shifts in the line centre were calculated to be less than 1 part in 10¹⁵. As a result of these measurements, the single trapped Sr⁺ ion is one of the most accurately known frequency standards in the visible region of the spectrum. We report here on its application to the measurement of two important optical frequencies.

© 2000 IEEE