Near-field focusing of dielectric microspheres: Super-resolution and field-invariant parameter scaling

TL;DR

This paper systematically investigates the focusing properties of dielectric microspheres, revealing super-resolution conditions and principles for field-invariant scaling, enabling super-resolution applications across the electromagnetic spectrum.

Contribution

It introduces a comprehensive analysis of super-resolution focusing in dielectric microspheres and establishes scaling principles for different particle sizes, refractive indices, and wavelengths.

Findings

Identification of super-resolution focal spots at least 50% below diffraction limit

Development of field-invariant parameter scaling laws

Demonstration of super-resolution applicability across the electromagnetic spectrum

Abstract

Optical near-fields of small dielectric particles are of particular importance and interests for nanoscale optical engineering such as field localization, fabrication, characterization, sensing and imaging. This paper represents a systematic investigation on the focusing characteristics (focal length, field enhancement, spot size) for a given refractive-index microsphere (n=1.6) with a varying size parameter across the range of pi<q0<20*pi. Conditions for super-resolution foci were analysised in details. Particularly strong super-resolution foci with spot size falling at least 50% below the diffraction limit were identified and possible new applications were suggested. To understand how the super-resolution conditions could be scaled to other refractive-index particles or background medium, principles of field-invariant parameters scaling (size, wavelength, and refractive index) were revealed and demonstrated with example cases. It offers the new freedom to choose particles and background medium to gain super-resolution at any frequency across the whole electromagnetic spectrum.