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“Plasmonics” in free space: observation of giant wavevectors, vortices, and energy backflow in superoscillatory optical fields

“Plasmonics” in free space: observation of giant wavevectors, vortices, and energy backflow in superoscillatory optical fields
“Plasmonics” in free space: observation of giant wavevectors, vortices, and energy backflow in superoscillatory optical fields

Evanescent light can be localized at the nanoscale by resonant absorption in a plasmonic nanoparticle or taper or by transmission through a nanohole. However, a conventional lens cannot focus free-space light beyond half of the wavelength λ. Nevertheless, precisely tailored interference of multiple waves can form a hotspot in free space of an arbitrarily small size, which is known as superoscillation. Here, we report a new type of integrated metasurface interferometry that allows for the first time mapping of fields with a deep subwavelength resolution ~λ/100. The findings reveal that an electromagnetic field near the superoscillatory hotspot has many features similar to those found near resonant plasmonic nanoparticles or nanoholes: the hotspots are surrounded by nanoscale phase singularities and zones where the phase of the superoscillatory field changes more than tenfold faster than a free-propagating plane wave. Areas with high local wavevectors are pinned to phase vortices and zones of energy backflow (~λ/20 in size) that contribute to tightening of the main focal spot size beyond the Abbe–Rayleigh limit. Our observations reveal some analogy between plasmonic nanofocusing of evanescent waves and superoscillatory nanofocusing of free-space waves and prove the fundamental link between superoscillations and superfocusing, offering new opportunities for nanoscale metrology and imaging.

2095-5545
1-9
Yuan, Guanghui
d7af6f06-7da9-41ef-b7f9-cfe09e55fcaa
Rogers, Edward T.F.
b92cc8ab-0d91-4b2e-b5c7-8a2f490a36a2
Zheludev, Nikolay I.
32fb6af7-97e4-4d11-bca6-805745e40cc6
Yuan, Guanghui
d7af6f06-7da9-41ef-b7f9-cfe09e55fcaa
Rogers, Edward T.F.
b92cc8ab-0d91-4b2e-b5c7-8a2f490a36a2
Zheludev, Nikolay I.
32fb6af7-97e4-4d11-bca6-805745e40cc6

Yuan, Guanghui, Rogers, Edward T.F. and Zheludev, Nikolay I. (2019) “Plasmonics” in free space: observation of giant wavevectors, vortices, and energy backflow in superoscillatory optical fields. Light: Science and Applications, 8 (1), 1-9, [2]. (doi:10.1038/s41377-018-0112-z).

Record type: Article

Abstract

Evanescent light can be localized at the nanoscale by resonant absorption in a plasmonic nanoparticle or taper or by transmission through a nanohole. However, a conventional lens cannot focus free-space light beyond half of the wavelength λ. Nevertheless, precisely tailored interference of multiple waves can form a hotspot in free space of an arbitrarily small size, which is known as superoscillation. Here, we report a new type of integrated metasurface interferometry that allows for the first time mapping of fields with a deep subwavelength resolution ~λ/100. The findings reveal that an electromagnetic field near the superoscillatory hotspot has many features similar to those found near resonant plasmonic nanoparticles or nanoholes: the hotspots are surrounded by nanoscale phase singularities and zones where the phase of the superoscillatory field changes more than tenfold faster than a free-propagating plane wave. Areas with high local wavevectors are pinned to phase vortices and zones of energy backflow (~λ/20 in size) that contribute to tightening of the main focal spot size beyond the Abbe–Rayleigh limit. Our observations reveal some analogy between plasmonic nanofocusing of evanescent waves and superoscillatory nanofocusing of free-space waves and prove the fundamental link between superoscillations and superfocusing, offering new opportunities for nanoscale metrology and imaging.

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More information

Accepted/In Press date: 3 December 2018
e-pub ahead of print date: 3 January 2019
Published date: 3 January 2019

Identifiers

Local EPrints ID: 427420
URI: http://eprints.soton.ac.uk/id/eprint/427420
ISSN: 2095-5545
PURE UUID: 972d1cce-337f-438a-b801-143b722252b4
ORCID for Nikolay I. Zheludev: ORCID iD orcid.org/0000-0002-1013-6636

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Date deposited: 16 Jan 2019 17:30
Last modified: 10 Jan 2022 02:35

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Contributors

Author: Guanghui Yuan
Author: Edward T.F. Rogers

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