High-resolution ultraviolet spectra of sympathetically-laser-cooledCd+ions

Cadmium ions (${\mathrm{Cd}}^{+}$) have been cooled sympathetically below 1 K by means of Coulomb interactions with laser-cooled ${\mathrm{Be}}^{+}$ ions that are trapped simultaneously in a Penning trap. The ultraviolet resonance lines (5${\mathit{s}}^{\mathrm{}2}$ ${\mathit{S}}_{1/2}$⇆5${\mathit{p}}^{\mathrm{}2}$ ${\mathit{P}}_{3/2}$, λ=214.5 nm) of the cooled ${\mathrm{Cd}}^{+}$ ions were observed using a frequency-doubled cw dye laser. This radiation is based on efficient frequency doubling in a nonlinear crystal [β-${\mathrm{BaB}}_2$ ${\mathrm{O}}_4$ (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.