title: Direct frequency-comb spectroscopy of a dipole-forbidden clock transition in trapped 40Ca+ ions.
abstract: We demonstrate direct frequency-comb (FC) spectroscopy of the dipole-forbidden 4s(2)S(1/2)-3d(2)D(5/2) transition in trapped (40)Ca(+) ions using an unamplified FC laser. The excitation is detected with nearly 100% efficiency using a shelving scheme in combination with single-ion imaging. The method demonstrated here has the potential to reach hertz-level accuracy, if a hertz-level linewidth FC is used in combination with confinement in the Lamb-Dicke regime.
authors.affiliation: LaserLaB Amsterdam (Institute for Lasers, Life and Biophotonics) Amsterdam, VU University De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
authors.forename: Anne Lisa
authors.initials: AL
authors.lastname: Wolf
authors.forename: Jonas
authors.initials: J
authors.lastname: Morgenweg
authors.forename: Jeroen C J
authors.initials: JC
authors.lastname: Koelemeij
authors.forename: Steven A
authors.initials: SA
authors.lastname: van den Berg
authors.forename: Wim
authors.initials: W
authors.lastname: Ubachs
authors.forename: Kjeld S E
authors.initials: KS
authors.lastname: Eikema