title: Anomalous Spectral Shift of Near- and Far-Field Plasmonic Resonances in Nanogaps.
abstract: The near-field and far-field spectral response of plasmonic systems are often assumed to be identical, due to the lack of methods that can directly compare and correlate both responses under similar environmental conditions. We develop a widely tunable optical technique to probe the near-field resonances within individual plasmonic nanostructures that can be directly compared to the corresponding far-field response. In tightly coupled nanoparticle-on-mirror constructs with nanometer-sized gaps we find >40 meV blue-shifts of the near-field compared to the dark-field scattering peak, which agrees with full electromagnetic simulations. Using a transformation optics approach, we show such shifts arise from the different spectral interference between different gap modes in the near- and far-field. The control and tuning of near-field and far-field responses demonstrated here is of paramount importance in the design of optical nanostructures for field-enhanced spectroscopy, as well as to control near-field activity monitored through the far-field of nano-optical devices.
authors.affiliation: NanoPhotonics Centre, Cavendish Laboratory, University of Cambridge , Cambridge, CB3 0HE, U.K.
authors.forename: Anna
authors.initials: A
authors.lastname: Lombardi
authors.affiliation: Centro de Física de Materiales, Centro Mixto CSIC-UPV/EHU, and Donostia International Physics Center (DIPC), Paseo Manuel Lardizabal 4, 20018 Donostia-San Sebastián, Spain; Blackett Laboratory, Department of Physics, Imperial College London, London SW7 2AZ, United Kingdom.
authors.forename: Angela
authors.initials: A
authors.lastname: Demetriadou
authors.affiliation: NanoPhotonics Centre, Cavendish Laboratory, University of Cambridge , Cambridge, CB3 0HE, U.K.
authors.forename: Lee
authors.initials: L
authors.lastname: Weller
authors.affiliation: NanoPhotonics Centre, Cavendish Laboratory, University of Cambridge , Cambridge, CB3 0HE, U.K.
authors.forename: Patrick
authors.initials: P
authors.lastname: Andrae
authors.affiliation: NanoPhotonics Centre, Cavendish Laboratory, University of Cambridge , Cambridge, CB3 0HE, U.K.
authors.forename: Felix
authors.initials: F
authors.lastname: Benz
authors.affiliation: NanoPhotonics Centre, Cavendish Laboratory, University of Cambridge , Cambridge, CB3 0HE, U.K.
authors.forename: Rohit
authors.initials: R
authors.lastname: Chikkaraddy
authors.affiliation: Centro de Física de Materiales, Centro Mixto CSIC-UPV/EHU, and Donostia International Physics Center (DIPC) , Paseo Manuel Lardizabal 4, 20018 Donostia-San Sebastián, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Aizpurua
authors.affiliation: NanoPhotonics Centre, Cavendish Laboratory, University of Cambridge , Cambridge, CB3 0HE, U.K.
authors.forename: Jeremy J
authors.initials: JJ
authors.lastname: Baumberg
keywords: SERS; nanoparticle on mirror; plasmonics; sensing; ultrafast tunable lasers