Cs-referenced optical frequency measurement of the single, trapped Sr/sup +/ ion standard at 445 THz

The frequency of the electric quadrupole allowed 5s/sup 2/S/sub 1/2/-4d/sup 2/D/sub 5/2/ transition at 445 THz in a single, trapped and laser cooled /sup 88/Sr/sup +/ ion has been measured with an optical frequency chain referenced to a Cs atomic clock. A transition frequency of f/sub S-D/=444 779 044 095.4 kHz with an estimated standard uncertainty of 0.2 kHz has been determined. The intrinsic offsets of the measured ion transition frequency due to environmental perturbations have been calculated to be at the 10/sup -15/ level.