Abstract

An azimuthally electric-polarized vector beam (APB), with a polarization vortex, has a salient feature that it contains a magnetic-dominant region within which the electric field is ideally null while the longitudinal magnetic field is maximum. Fresnel diffraction theory and plane-wave spectral calculations are applied to quantify field features of such a beam upon focusing through a lens. The diffraction-limited full width at half-maximum (FWHM) of the beam’s longitudinal magnetic field intensity profile and complementary FWHM of the beam’s annular-shaped total electric field intensity profile are examined at the lens’s focal plane as a function of the lens’s paraxial focal distance. Then, we place a subwavelength dense dielectric Mie scatterer in the minimum-waist plane of a self-standing converging APB and demonstrate for the first time, to the best of our knowledge, that a very-high-resolution magnetic near-field at optical frequency is achieved with total magnetic near-field FWHM of $0.23\lambda$ (i.e., magnetic near-field spot area of $0.04{\lambda }^2$) within a magnetic-dominant region located one radius ($0.12\lambda$) away from the scatterer. In particular, the utilization of the nanosphere as a magnetic nanoantenna (so-called magnetic nanoprobe) illuminated by a tightly focused APB is instrumental in boosting the photoinduced magnetic response and suppressing the electric response of a sample matter. The access to the weak photoinduced magnetic response in sample matter would add extra degrees of freedom to future optical photoinduced force microscopy and spectroscopy systems based on the excitation of photoinduced magnetic dipolar transitions.

© 2016 Optical Society of America

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