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 Be⁺ ions that are trapped simultaneously in a Penning trap. The ultraviolet resonance lines (5s ²S_1/2⇆5p ²P_3/2, λ=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 [β-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. © 1996 The American Physical Society.