High-resolution ultraviolet spectra of sympathetically-laser-cooled Cd+ ions

Cadmium ions (Cd+) have been cooled sympathetically below 1 K by means of Coulomb interactions with laser-cooled Bet ions that are trapped simultaneously in a Penning trap. The ultraviolet resonance lines (5s S-2(1/2)<----> 5p P-2(3/2), lambda = 214.5 nm) of the cooled Cd+ ions were observed using a frequency-doubled cw dye laser. This radiation is based on efficient frequency doubling in a nonlinear crystal [beta-BaB2O4 (BBO)] with an external enhancement cavity. The spectra of the six isotopes (A = 110-114, and 116) were obtained using a natural isotope mixture, and the reliability of the measured isotope shifts is discussed.