Localizing light
to nanoscale volumes through nanoscale resonators
that are low loss and precisely tailored in spectrum to properties
of matter is crucial for classical and quantum light sources, cavity
QED, molecular spectroscopy, and many other applications. To date,
two opposite strategies have been identified: to use either plasmonics
with deep subwavelength confinement yet high loss and very poor spectral
control or instead microcavities with exquisite quality factors yet
poor confinement. In this work we realize hybrid plasmonic–photonic
resonators that enhance the emission of single quantum dots, profiting
from both plasmonic confinement and microcavity quality factors. Our
experiments directly demonstrate how cavity and antenna jointly realize
large cooperative Purcell enhancements through interferences. These
can be controlled to engineer arbitrary Fano lineshapes in the local
density of optical states.
Electromagnetically induced transparency in metamaterials allows to engineer structures which transmit narrow spectral ranges of radiation while exhibiting a large group index. Implementation of this phenomenon frequently calls for strong near-field coupling of bright (dipolar) resonances to dark (multipolar) resonances in the metamolecules comprising the metamaterials. The sharpness and contrast of the resulting transparency windows thus depends strongly on how closely these metamolecules can be placed to one another, placing constraints on fabrication capabilities. In this manuscript, we demonstrate that the reliance on near-field interaction strength can be relaxed, and the magnitude of the electromagnetic-induced transparency enhanced, by exploiting the long-range coupling between metamolecules in periodic lattices. By placing dolmen structures resonant at THz frequencies in a periodic lattice, we show a significant increase of the transparency window when the in-plane diffraction is tuned to the resonant frequency of the metamolecules, as confirmed by direct mapping of the THz near-field amplitude across a lattice of dolmens. Through the direct interrogation of the dark resonance in the near field, we show the interplay of near-and far-field couplings in optimizing the response of planar dolmen arrays via diffraction-enhanced transparency.
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We report an experimental technique for determining phase-resolved radiation patterns of single nanoantennas by phase-retrieval defocused imaging. A key property of nanoantennas is their ability to imprint spatial coherence, for instance, on fluorescent sources. Yet, measuring emitted wavefronts in absence of a reference field is difficult. We realize a defocused back focal plane microscope to measure phase even for partially temporally coherent light and benchmark the method using plasmonic bullseye antenna scattering. We outline the limitations of defocused imaging which are set by spectral bandwidth and antenna mode structure. This work is a first step to resolve wavefronts from fluorescence controlled by nanoantennas.
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