title: Excitation of magnetic dipole transitions at optical frequencies.
abstract: We use the magnetic field distribution of an azimuthally polarized focused laser beam to excite a magnetic dipole transition in Eu^{3+} ions embedded in a Y2O3 nanoparticle. The absence of the electric field at the focus of an azimuthally polarized beam allows us to unambiguously demonstrate that the nanoparticle is excited by the magnetic dipole transition near 527.5 nm. When the laser wavelength is resonant with the magnetic dipole transition, the nanoparticle maps the local magnetic field distribution, whereas when the laser wavelength is resonant with an electric dipole transition, the nanoparticle is sensitive to the local electric field. Hence, by tuning the excitation wavelength, we can selectively excite magnetic or electric dipole transitions through optical fields.
authors.affiliation: Photonics Laboratory, ETH Zürich, 8093 Zürich, Switzerland.
authors.forename: Mark
authors.initials: M
authors.lastname: Kasperczyk
authors.affiliation: Institute of Optics, University of Rochester, Rochester, New York 14627, USA.
authors.forename: Steven
authors.initials: S
authors.lastname: Person
authors.affiliation: Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Duarte
authors.initials: D
authors.lastname: Ananias
authors.affiliation: Department of Physics, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Luis D
authors.initials: LD
authors.lastname: Carlos
authors.affiliation: Photonics Laboratory, ETH Zürich, 8093 Zürich, Switzerland.
authors.forename: Lukas
authors.initials: L
authors.lastname: Novotny