Abstract

We report recent improvement in absolute frequency measurement of the ¹¹⁵In⁺ 5s^{2 1}S₀−5s5p ³P₀ clock transition at 236.5 nm. Using a narrowline laser as a local oscillator, a linewidth of 43 Hz for the transition is resolved, as shown in Fig. la. The uncertainty of the transition frequency's centroid is 18 Hz, leading to a fractional uncertainty of 1.4 × 10⁻¹⁴. In the experiment, a single ¹¹⁵In⁺ is trapped in a three-ring Paul-Straubel trap and laser cooled to the trap's vibrational ground states. A monolithic, isolated, end-pumped ring Nd: YAG clock laser (MISER, 946 nm), locked to a high finesse, ultra-low expansion cavity, serves as the master local oscillator. Its fourth harmonic at 236.5 nm is scanned through the 5s^{2 1}S₀−5s5p ³P₀ clock transition and the resonance is detected using the electron shelving method, by detecting the fluorescence signal of the 5s^{2 1}S₀−5s5p ³P₁ cooling transition.

© 2007 IEEE