Application of the Continuous Stern-Gerlach Effect for Laser Spectroscopy of the 40Ar13+ Fine Structure in a Penning Trap

We report on the successful demonstration of a novel scheme for detecting optical transitions in highly charged ions. We applied it to determine the frequency of the dipole-forbidden 2p P-2(1/2) - P-2(3/2) transition in the fine structure of Ar-40(13+) using a single ion stored in the harmonic potential of a Penning trap. Our measurement scheme does not require detection of fluorescence, instead it makes use of the continuous Stern-Gerlach effect. Our value of 679.216464(4)(stat) (5)(syst) THz is in reasonable agreement with the current best literature values and improves its uncertainty by a factor of 24.