Development of an indium ion optical frequency standard

We report on the progress toward an indium ion optical frequency standard with an expected accuracy of 10^-18. A ¹¹⁵In⁺ has been successfully prepared by sympathetic cooling with two laser-cooled ⁴⁰Ca⁺ 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 the ¹S₀-³P₁ transition at 230 nm.