Multipolar and dark-mode plasmon resonances on drilled silver nano-triangles

Wavelength-Dependent Optical Nonlinear Absorption of Au-Ag Nanoparticles

The nonlinear optical absorption properties of Au-Ag nanoparticles (NPs) were studied using an open-aperture Z-scan under a nanosecond pulsed laser with wavelengths of 450 nm, 510 nm, 550 nm, and 600 nm. The experimental results demonstrated that, when the laser intensity was 1.04 × 1013 W/m2, the Au-Ag NPs showed saturated absorption (SA). When the laser intensity was increased to 3.03 × 1013 W/m2, the switch from SA to reverse saturation absorption (RSA) occurred. The nonlinear absorption and its transformation were analyzed by using local surface plasmon resonance (LSPR) effect, bleaching of ground state plasmon, and free carrier absorption theory.

Superior Resonant Nanocavities Engineering on the Photonic Crystal-Coupled Emission Platform for the Detection of Femtomolar Iodide and Zeptomolar Cortisol

Although luminescence spectroscopy has been a promising sensing technology with widespread applications in point-of-care diagnostics and chem-bio detection, it fundamentally suffers from low signal collection efficiency, considerable background noise, poor photostability, and intrinsic omnidirectional emission properties. In this regard, surface plasmon-coupled emission, a versatile plasmon-enhanced detection platform with >50% signal collection efficiency, high directionality, and polarization has previously been explored to amplify the limit of detection of desired analytes. However, high Ohmic loss in metal-dependent plasmonic platforms has remained an inevitable challenge. Here, we develop a hybrid nanocavity interface on a template-free and loss-less photonic crystal-coupled emission (PCCE) platform by the quintessential integration of high refractive index dielectric Nd₂O₃ "Huygens sources" and sharp-edged silver nanoprisms (NPrs). While efficient forward light scattering characteristics of Nd₂O₃ nanorods (NRs) present 460-fold emission enhancements in PCCE, the tunable localized plasmon resonances of NPrs display high electromagnetic field confinement at sharp nanotips and protrusions, boosting the enhancements 947-fold. The judicious use of silver NPr (AgNPr) metal-Nd₂O₃ dielectric hybrid resonances in conjugation with surface-trapped Bloch surface waves of the one-dimensional photonic crystal (1DPhC) displayed unprecedented >1300-fold enhancements. The experimental results are validated by excellent correlations with numerical calculations. The multifold hotspots generated by zero and nonzero nanogaps between the coassembly of NPrs, NRs, and 1DPhCs are used for (i) determination of hyper and hypothyroidism levels through monitoring the concentration of iodide (I^-) ions and (ii) single-molecule detection (zeptomolar) of the stress hormone, cortisol, through the synthesized cortisol-rhodamine B conjugate obtained using a simple esterification reaction.

Radiation of Dynamic Toroidal Moments

Dynamic toroidal dipoles, a distinguished class of fundamental electromagnetic sources, receive increasing interest and participate in fascinating electrodynamic phenomena and sensing applications. As described in the literature, the radiative nature of dynamic toroidal dipoles is sometimes confounded, intermixing with static toroidal dipoles and plasmonic dark modes. Here, we elucidate this issue and provide proof-of-principle experiments exclusively on the radiation behavior of dynamic toroidal moments. Optical toroidal modes in plasmonic heptamer nanocavities are analyzed by electron energy loss spectroscopy and energy-filtered transmission electron microscopy supported by finite-difference time-domain numerical calculations. Additionally, their corresponding radiation behaviors are experimentally investigated by means of cathodoluminescence. The observed contrasting behaviors of a single dynamic toroidal dipole mode and an antiparallel toroidal dipole pair mode are discussed and elucidated. Our findings further clarify the electromagnetic properties of dynamic toroidal dipoles and serve as important guidance for the use of toroidal dipole moments in future applications.

Influence of the external field on the excitation properties of plasmon in linear atomic chain

Based on the self-consistent linear response theory, the plasmon-energy absorption in linear atomic chain are studied by using the tight-binding approximation. Results indicate that the eigen-frequency of the plasmon is uninfluenced by the external electric potential, but the plasmon modes excited by various electric potentials are obviously different. Each mode of plasmon corresponds to one kind of eigen-charge distribution. When the plasmon mode is excited, the resonant charge will show a distribution characteristic the same as the one of eigen charge. And the plasmon mode can be precisely controlled by external electric potential if the eigen-charge distribution at such plasmon is known. The relationship between plasmon-energy absorption and atom number are also affected by the external electric potential. However, most of the other studies only show the normal case that the plasmon-energy absorption increases with the atom number increasing. Here, we demonstrate that the normal case commonly occurs under monotone increasing potential. And abnormal case may occur under monotone decreasing potential, ie, the plasmon-energy absorption will decrease with the atom number increasing. But, in the presence of arbitrary potential applied to the same atomic chain, the plasmon-energy absorption will always increase with the electron number increasing.

Generating and Manipulating High Quality Factors of Fano Resonance in Nanoring Resonator by Stacking a Half Nanoring

We demonstrate the existence of Fano resonance spectral response in a system of nanoscale plasmonic resonant ring stacked by means of a half nanoring. Our proposed scheme exploits the stacked method under normal incidence to excite the subradiant mode. The nanostructure, which utilizes the combination of Fano resonance and polarization-resolved, has a new rotation mode and high tunability, providing a dynamic control of plasmonic spectral response. High-quality resonant line shapes corresponding to the different order modes of Fano structures are readily achieved at near-infrared wavelengths, which is a benefit to the application for nanosensor in highly integrated circuits.

Enhanced Third Harmonic Generation in Single Germanium Nanodisks Excited at the Anapole Mode

We present an all-dielectric germanium nanosystem exhibiting a strong third order nonlinear response and efficient third harmonic generation in the optical regime. A thin germanium nanodisk shows a pronounced valley in its scattering cross section at the dark anapole mode, while the electric field energy inside the disk is maximized due to high confinement within the dielectric. We investigate the dependence of the third harmonic signal on disk size and pump wavelength to reveal the nature of the anapole mode. Each germanium nanodisk generates a high effective third order susceptibility of χ((3)) = 4.3 × 10(-9) esu, corresponding to an associated third harmonic conversion efficiency of 0.0001% at an excitation wavelength of 1650 nm, which is 4 orders of magnitude greater than the case of an unstructured germanium reference film. Furthermore, the nonlinear conversion via the anapole mode outperforms that via the radiative dipolar resonances by about 1 order of magnitude, which is consistent with our numerical simulations. These findings open new possibilities for the optimization of upconversion processes on the nanoscale through the appropriate engineering of suitable dielectric materials.

Role of multipolar plasmon resonances during surface-enhanced Raman spectroscopy on Au micro-patches

Large more reproducibly fabricated microstructures can also provide significant Raman signal enhancementviausually neglected multipolar plasmon resonances.

Modal engineering of Surface Plasmons in apertured Au Nanoprisms

Crystalline gold nanoprisms of sub-micrometric size sustain high order plasmon modes in the visible and near infrared range that open a new realm for plasmon modal design, integrated coplanar devices and logic gates. In this article, we explore the tailoring of the surface plasmon local density of states (SP-LDOS) by embedding a single defect, namely a small hole, carved in the platelet by focused ion beam (FIB). The change in the SP-LDOS of the hybrid structure is monitored by two-photon luminescence (TPL) microscopy. The dependency of the two-dimensional optical field intensity maps on the linear polarization of the tightly focused femtosecond laser beam reveals the conditions for which the hole defect significantly affects the initial modes. A detailed numerical analysis of the spectral characteristics of the SP-LDOS based on the Green dyadic method clearly indicates that the hole size and location can be exploited to tune or remove selected SP modes.