Photonic nanojets as emergent free-space power flux funnels

TL;DR

This paper introduces a mesoscopic model for photonic nanojets that explains their formation as free-space power flux funnels, providing new insights and design principles for nano-optics applications.

Contribution

It presents a reduced local field model linking full-wave simulations to a free-space mode structure, advancing understanding of nanojet formation and confinement.

Findings

Quantitative nanojet morphology prediction

Geometry-independent lower bound on nanojet waist

Connection between Maxwell fields and free-space oscillator model

Abstract

A reduced local field model derived from full-wave electromagnetic simulations shows that photonic nanojet formation corresponds to an emergent mesoscopic funnel of propagating power flux sustained by an effective free-space transverse mode structure. This interpretation moves beyond purely geometric-optics or interference-based explanations by identifying a self-consistent redistribution of phase gradients and effective longitudinal wavenumber near the nanojet waist. The model quantitatively captures characteristic nanojet morphology, including the formation and local structure of the jet waist. It also yields a geometry-independent lower bound on the nanojet waist, linking transverse confinement to the effective axial wavenumber through an explicit trade-off. The model establishes a direct connection between full-wave Maxwell fields and a reduced free-space oscillator description, yielding new physical insight into nanojet confinement and suggesting design principles for nanojet-assisted imaging, lithography, and subwavelength field localization.