High-resolution spectroscopy of a single In+ ion:: Progress towards an optical frequency standard -: art. no. 051082

The 5s(2 1)S(0)--> 5s5p P-3(0) transition of a single laser-cooled In-115(+) ion in a miniature radiofrequency trap is investigated as a possible optical frequency standard. This line at a frequency of 1267 THz (wavelength 236.5 nm) is highly immune to frequency shifts due to external perturbations so that the expected systematic uncertainties can be reduced to the millihertz level. Experimentally. we obtained a fractional resolution Deltav/v = 1.3 x 10(-13) (linewidth 170 Hz), limited by the frequency instability of the laser used for excitation. The g factor and the lifetime of the metastable P-3(0) level were measured as g(P-3(0)) = -9.87(5) x 10(-4) and tau(P-3(0)) = 0.195(8) s. Both values are in good agreement with perturbative calculations, based an hyperfine mixing between the P-1 and P-3 levels.