Plasmonic topological insulators using dual layer hexagonal complementary structure provide TE/TM pseudospin edge states. We use finite-difference time-domain method to analyze its nontrivial band structure and the transmission efficiency of topological protected edges states. Chern numbers are calculated by both Berry curvature and Willson loop method. The effect of defects, sharp bendings and scattering loss in one-way transmission are also discussed.
Chiral Plasmonics is a new and hot research topics, which studies the different in optical responses to the incident light with different handedness. Many new and exciting concepts have been reported in the literature; however, fabrication of these chiral nanostructures is not an easy task. It is especially hard to fabricate three-dimensional chiral nanostructures that cover large area and with high enough throughput.
In this study, we will demonstrate he fabrication of various chiral nanostructures using a method combining various nanofabrication technique, including Nanospherical-Lens Lithography (NLL), Nano-Stencil Lithography (NSL) and Hole Mask Lithography (HML). NLL is a technique that has been developed in our group for years and has been demonstrated to be able to integrated with HML to fabricated complicated nanostructures. In this investigation, we study the possibility to integrated the NSL and the HML so we are able to fabricate more nanostructures that can not be fabricated using NLL.
Finally, we will investigate the optical properties of the fabricated chiral nanostructures using three-dimensional finite difference time-domain method. Experimental measurements will also be performed to understand the actual optical properties of the fabricated nanostructures. In the end, we will use these chiral nanostructures to detect some chiral molecules.
Avoided resonance crossing [1] is a general phenomenon occurring in almost all physical interactions. It describes the splitting behavior in a coupled system. For example, in dielectric hexagonal dielectric resonators [2], the degenerated triangular resonant modes exhibit energy level and line-width anti-crossing by varying the height of one hexagonal edge. One of the modes leads to longer life time with higher quality factor. Whether the energy level or line-width exhibits either crossing or anti-crossing depends on the mechanism of interaction [1,2]. In this paper, we show that similar anti-resonance crossing behavior can be observed in plasmonic nanostructures due to either near field or far field coupling. Near field coupling in disk dimmer can lead to both energy and line-width anti-crossing. This anti-crossing phenomena can also be explained by simple Hamiltonian model [1,2] and we show the corresponding phenomena for both vertically and horizontally aligned two disks. By varying the size of one disk as the hetero-dimer approaching homo-dimer, the anti-crossing in both energy and linewidth appears. The Hamiltonian model also predicts the energy crossing and linewidth anticrossing for far field coupling. However, there is little literature discussion on the avoided crossing by far field coupling in plasmonic structure.
In this work we found that far field coupling in double layered disk array with gap size close to Fabry-Perot (FP) resonant condition leads to line-width anti-crossing but energy crossing by varying either the gap size or the diameter of one disk. Asymmetric reflection and absorption spectra from different side of the double layered disk arrays with asymmetric disk arrays (or disk arrays without mirror system) show the disappearing of Fabry-Perot resonant mode and non-reciprocal perfect absorption properties. This nearly perfect absorption is fundamentally connected to the anti-crossing phenomena in asymmetric disk arrays. We use a simple frequency-selective surface (FSS) model to represent the individual disk array and use the FP model to connect the tow arrays. This simple FSS-FP model matches well with the full wave finite-different time-domain modeling. This model can also explain the perfect absorption properties for ultra-thin metamaterial surface observed in literature. The observed avoided resonance crossings and nonreciprocal absorption in plasmonic nanostructure would lead to many photonics applications such as high Q resonators for future sensing applications.
This study investigated theoretically and experimentally that two-photon excited fluorescence is enhanced and
quenched via surface plasmons (SPs) excited by total internal reflection with a silver film. The fluorescence intensity is
fundamentally affected by the local electromagnetic field enhancement and the quantum yield change according to the
surrounding structure and materials. By utilizing the Fresnel equation and classical dipole radiation modeling, local
electric field enhancement, fluorescence quantum yield, and fluorescence emission coupling yield via SPs were
theoretically analyzed at different dielectric spacer thicknesses between the fluorescence dye and the metal film. The
fluorescence lifetime was also decreased substantially via the quenching effect. A two-photon excited total internal
reflection fluorescence (TIRF) microscopy with a time-correlated single photon counting device has been developed to
measure the fluorescence lifetimes, photostabilities, and enhancements. The experimental results demonstrate that the
fluorescence lifetimes and the trend of the enhancements are consistent with the theoretical analysis. The maximum
fluorescence enhancement factor in the surface plasmon-total internal reflection fluorescence (SP-TIRF) configuration
can be increased up to 30 fold with a suitable thickness SiO2 spacer. Also, to compromise for the fluorescence
enhancement and the fluorophore photostability, we find that the SP-TIRF configuration with a 10 nm SiO2 spacer can
provide an enhanced and less photobleached fluorescent signal via the assistance of enhanced local electromagnetic
field and quenched fluorescence lifetime, respectively.
We study surface-enhanced infrared absorption, including multiphoton processes, due to the excitation of surface
plasmons on metal nanoparticles. The time-dependent Schroedinger equation and finite-difference time-domain method
are self-consistently coupled to treat the problem.
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