Abstract
The concept of magnetic nanoprobes (or magnetic nanoantennas), their excitation, and the capability of providing a magnetic near-field enhancement and vanishing electric field is presented and investigated. It is established that a particular type of cylindrical vector beam called an azimuthally electric polarized vector beam yields a strong longitudinal magnetic field on the beam axis where the electric field is ideally null. These beams, with an electric polarization vortex and cylindrical symmetry, are important in generating high magnetic to electric field contrast, i.e., large local field admittance, and in allowing selective excitation of magnetic transitions in matter located on the beam axis. We demonstrate that azimuthally polarized vector beam excitation of a photoinduced magnetic nanoprobe made of a magnetically polarizable nanocluster leads to an enhanced magnetic near field with resolution beyond the diffraction limit. We introduce two figures of merit, magnetic field enhancement and local fi...
Highlights
NATURAL magnetism at optical frequencies is rather weak when compared to electric response of matter [1]
We have shown that the normalized absolute local field admittance FY around the center of the nano cluster excited by the azimuthally polarized beam (APB) is ideally very large alongside a magnetic field enhancement FH around 4.2
We demonstrate that large magnetic field enhancement is robust to small physical defects in the nano cluster and to small misalignments of the APB with respect to the cluster’s center, though the latter decreases the local field admittance
Summary
NATURAL magnetism at optical frequencies is rather weak when compared to electric response of matter [1]. The utilization of a magnetic nanoprobe for enhancing the magnetic transitions and suppressing the electric dipolar ones in matter requires: (i) excitation of the magnetic mode of the nanoprobe leading to enhanced magnetic near field, (ii) suppressing the electric near field where magnetic field is enhanced. To help in the latter magnetic to electric field contrast aspect, symmetry in the magnetic nanoprobe and in its excitation plays an important role as we show in this paper.
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