Skip to main content
eScholarship
Open Access Publications from the University of California

UC Irvine

UC Irvine Previously Published Works bannerUC Irvine

Focused azimuthally polarized vector beam and spatial magnetic resolution below the diffraction limit

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 0.23λ (i.e., magnetic near-field spot area of 0.04λ2) within a magnetic-dominant region located one radius (0.12λ) 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 photoin duced 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 photo induced force microscopy and spectroscopy systems based on the excitation of photoinduced magnetic dipolar transitions.

Many UC-authored scholarly publications are freely available on this site because of the UC's open access policies. Let us know how this access is important for you.

Main Content
For improved accessibility of PDF content, download the file to your device.
Current View