Enhancing resonances of optical nanoantennas by circular gratings

Abstract

Optical plasmonic antennas allow for localizing and enhancing light at the nanoscale. To enhance the application opportunities of optical antennas, their quality factor needs to be substantially improved. Here, we numerically and experimentally demonstrate that the resonance of a dipolar metallic disc antenna can be enhanced by a circular grating that obeys the Bragg condition. The supporting grating effectively collects energy from an extended spatial domain and guides it spectrally-selected into the central antenna, leading to a significantly enhanced field intensity at resonance. Accordingly, the quality factor of the antenna is enhanced by at least five times. The approach can be applied to other plasmonic systems, hence constituting an important ingredient to a future plasmonic tool box. References and links1. L. Novotny and N. van Hulst, "Antennas for light," Nature Photon. 5, 83-90 (2011). 2. P. Bharadwaj, B. Deutsch, and L. Novotny, "Optical antennas," Adv. Opt. Photon. 1(3), 438-483 (2009)

Characterization of a circular optical nanoantenna by nonlinear photoemission electron microscopy

“…In this work, we wish to investigate the behavior of a circular optical nanoantenna under ultrafast excitation using nonlinear PEEM at near-normal incidence. The resonance of the antenna was enhanced by a properly designed surrounding grating [7]. We find a pronounced enhancement of the photoelectron yield both for TE and TM polarization of the incident light.…”

“…The resonance strength of a nanoantenna can be increased significantly when the central element is enclosed by a periodic structure [7,38]. The configuration acts as a Bragg reflector if concentric rings are used in our case to enclose the central nanodisc.…”

“…Such an approach does not require phase matching to the Hankel modes and can be used to excite the disc at any wavelength within the bandwidth of its localized plasmonic resonance. However, it is also possible to employ the grating to couple incident light resonantly into Hankel plasmons [7]. The prerequisite for this is known as the Bloch condition and reads as…”

“…Our design approach originates from the simple observation that (6) and (7) can be fulfilled simultaneously for certain combinations of θ, m, and n if…”

Polarization-Dependent Quasi-Far-Field Superfocusing Strategy of Nanoring-Based Plasmonic Lenses

“…Additionally, utilizing a donut-shape aperture stop [26, 27] or Fresnel zone plate [28], this polarized light has been applied to realize the subwavelength circular-shape focus. Thus, the radially polarized light was generally applied as the incident light of NRPLs [20–23]. Compared with the subwavelength focusing with the spatial filter, these PLs possess the ability to modulate the phase of incident light in the subwavelength waveguide.…”