Abstract

Optical frequency magnetic dipole (MD) transitions follow different selection rules from those invoked by the coupling of light to the electric dipole (ED) moment giving valuable complementary spectral information about the system under investigation. However, MD interactions contribute to the optical spectrum by approximately two orders of magnitude less than the ED transitions, therefore remaining concealed in traditional optical spectroscopy. To allow the unperturbed direct detection of the magnetic-field–MD interactions a novel type of magneto-optical spectroscopy is proposed. To this end, spatial separation of the electric and the magnetic field (EF & MF) components of the light can be achieved by means of azimuthally polarised beams (APB) [1]. Under external focusing, the APB develops a doughnut-shaped intensity profile exhibiting a longitudinal MF component at the centre of the beam while the polarisation of the EF oscillates along the beam perimeter. Another way to discern between ED and MD transitions is through spectral selectivity. For example, Eu³⁺ ions exhibit a MD-allowed transition at 527.5 nm and an ED-allowed one at 532 nm [2].

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