Beyond-limit light focusing in the intermediate zone

TL;DR

This paper demonstrates experimentally that a plasmonic nanolens can focus light into a line narrower than the diffraction limit in the intermediate zone, with the focused fields being radiative and capable of propagating to the far zone.

Contribution

It introduces a novel plasmonic nanolens design that achieves sub-diffraction-limit line focusing in the intermediate zone, confirming theoretical predictions about radiative fields.

Findings

Achieved line widths beyond the diffraction limit in the intermediate zone

Focused fields are radiative and capable of propagating to the far zone

Near-field effects are negligible in the intermediate zone

Abstract

We experimentally demonstrate that a new nanolens of designed plasmonic subwavelength aperture can focus light to a single-line with its width beyond the diffraction limit that sets the smallest achievable line width at half the wavelength. The measurements indicate that the effect of the near-field on the light focused is negligible in the intermediate zone of 2 < kr < 4 where the line-width is smaller than the limit. Thus, as a verification of theoretical prediction, the fields focused are radiative and with a momentum capable of propagating to the far zone as concerned by the limit.