Shaping Field Gradients for Nanolocalization

TL;DR

This paper demonstrates that engineering electromagnetic field gradients enhances the sensitivity of nanolocalization techniques, enabling more precise detection of nanoantenna displacements through far-field polarization segmentation.

Contribution

It introduces a novel localization scheme utilizing transverse spin fields and field gradient sculpting to improve displacement sensitivity in nanometrology.

Findings

Enhanced sensitivity achieved with vector beams having increased transverse spin density gradients.

Experimental confirmation of improved far-field spin-segmentation sensitivity to nanoantenna displacements.

Field gradient sculpting and scatterer design are key to advancing nanolocalization precision.

Abstract

Deep sub-wavelength localization and displacement sensing of optical nanoantennas have emerged as extensively pursued objectives in nanometrology, where focused beams serve as high-precision optical rulers while the scattered light provides an optical readout. Here, we show that in these schemes using an optical excitation as a position gauge implies that the sensitivity to displacements of a nanoantenna depends on the spatial gradients of the excitation field. Specifically, we explore one of such novel localization schemes based on appearance of transversely spinning fields in strongly confined optical beams, resulting in far-field segmentation of left- and right-hand circular polarizations of the scattered light, an effect known as the giant spin-Hall effect of light. We construct vector beams with augmented transverse spin density gradient in the focal plane and experimentally confirm enhanced sensitivity of the far-field spin-segmentation to lateral displacements of an electric-dipole nanoantenna. We conclude that sculpturing of electromagnetic field gradients and intelligent design of scatterers pave the way towards future improvements in displacement sensitivity.