2 research outputs found
Metal–Dielectric Hybrid Dimer Nanoantenna: Coupling between Surface Plasmons and Dielectric Resonances for Fluorescence Enhancement
Dimers
made of noble metal particles possess extraordinary field
enhancements but suffer from large dissipation, whereas low-loss dielectric
dimers are limited by relatively weak optical confinement. Hybrid
systems could take advantages from both worlds. In this contribution,
we study the mode coupling in a hybrid dimer with rigorous dipole–dipole
interaction theory and explore its potential in fluorescence enhancement.
We first discovered that the direct coupling between metal surface–plasmon
resonance and dielectric electric–dipole mode creates a hybridized
mode due to the strong electric–electric dipole–dipole
interaction between the constituent nanoparticles, whereas the dielectric
magnetic–dipole mode can only indirectly couple to the plasmons
on the basis of the induced electric–magnetic dipole–dipole
interaction. When an electric/magnetic quantum emitter couples to
the hybrid dimer, the emitter selectively excites the electric/magnetic
(magnetic/electric) resonant modes of the dimer for emitter orientation
parallel (perpendicular) to the dimer axis. Our study shows that the
hybrid dimer simultaneously possesses high field enhancement and low-loss
features, which demonstrates a fluorescence excitation rate 40% higher
than that of the pure dielectric dimer and an average quantum yield
30% higher than that of the pure metallic dimer. On top of that, the
unique asymmetrical structure of the hybrid dimer directs 20% more
radiation toward the dielectric side, hence improving the directivity
of the dimer as an antenna
Hybrid Mushroom Nanoantenna for Fluorescence Enhancement by Matching the Stokes Shift of the Emitter
Nanoantenna-enhanced
fluorescence is a promising method in many
emergent applications, such as single molecule detection. The excitation
and emission wavelengths of emitters can be well separated depending
on the corresponding Stokes shifts, preventing optimal fluorescence
enhancement by a rudimentary nanoantenna. We illustrate a hybrid mushroom
nanoantenna that can achieve overall enhancements (e.g., excitation
rate, quantum yield, fluorescence enhancement) in fluorescence emission.
The nanoantenna is made of a plasmonic metal stipe and a dielectric
cap, and the resonances can be flexibly and independently controlled
to match the Stokes shift of the emitter. By fully leveraging the
advantages of the large field enhancement from the metal and the low
loss feature from the dielectric, a fluorescence enhancement factor
(far field intensity) twice (20 times) as high as that from a pure
metallic antenna can be attained, accompanied by improved directivity.
Approximately 70% of the overall radiation was directed toward the
mushroom cap via coupling to the dielectric resonance, which could
benefit the collection efficiency. This hybrid concept introduces
a way to build high-performance nanoantennas for fluorescence enhancement
applications