Progress toward a single indium ion optical frequency standard

We report an improved absolute frequency measurement of the 5s(2) S-1(0) - 5s5p P-3(0) narrowline clock transition at 236.5 nm, for a single trapped and laser cooled In-115(+). Using a narrowline laser as the local oscillator, a linewidth of 43 Hz for the transition is resolved. For absolute frequency measurement we use an optical frequency comb referenced to a cesium clock The transition frequency is found to be 1, 267, 402, 452, 900, 967 (63) Hz, averaged over 13 days of separate measurements. The accuracy is about 5.0 X 10(-14). And a preliminary absolute frequency measurement is shown with a Hydrogen maser as the reference. We discuss possibilities for further improvement.