Laser cooling and quantum jumps of a single indium ion

We performed laser spectroscopy of In⁺ ions stored in a radio-frequency trap. The 5s² ¹{S}₀→5s5p³P₁ transition at 230.6 nm was excited and its hyperfine splitting and isotope shift have been measured. The lifetime of the ³{P}₁state was measured using intensity modulated laser excitation: τ{(}³P₁)=0.44(4) {μ}s. A single indium ion was laser cooled using this intercombination line and dark periods in the fluorescence were observed when the metastable ³{P}₀$ state was populated by a magnetic dipole decay from $³P₁. The radiative lifetime of the forbidden transition ³{P}₀→¹{S}₀was determined from the duration of the dark periods: τ{(}³P₀)=0.14(2) s. This value is compared to calculations based on perturbation theory. Prospects for an optical frequency standard using the narrow 5s² ¹{S}₀→5s5p³P₀ resonance at 236.5 nm of a single laser-cooled indium ion are discussed.