This PDF file contains the front matter associated with SPIE Proceedings Volume 10028 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Strong coupling of metallic nanoparticles results in interaction of the plasmonic properties of individual nanoparticles and forms a new hybridized response that can be controlled through nanoparticle geometry and excitation field parameters. In this report, we show controlled excitation and enhancement of gap plasmon responses in closely spaced and differently aligned gold nanoparticles of various sizes and shapes. Our numerical results reveal that the spectral, spatial, and temporal intensities of coupled nanoparticles can be hugely enhanced by controlling the geometry, morphology, and alignment of the nanoparticles. Besides, shaping the temporal profiles of the excitation field gives an unprecedented control over the spectral and temporal responses of the gap plasmons. These findings might have implications for designing and fabrication of metallic nanoparticles for surface-based applications.

A metal-insulator-metal (MIM) structure is a fundamental plasmonic structure that has been studied widely since the early stage of plasmonics. It enables us to confine surface plasmon polariton (SPP) and concentrate light into nano-space beyond the diffraction limit. A finite-length MIM structure is considered to be a Fabry-Perot resonator of SPP as a nanocavity. Here, we review our recent studies about active metasurface based on a reconfigurable metal-air-metal (MAM) nanocavity which modify reflection or absorption spectra in scattering by changing a gap distance. Such reconfigurable MAM nanocavity becomes promising candidate for various applications such as plasmonic color or sky radiator from visible to infrared range.

Surface-enhanced Raman scattering (SERS) is an effective spectral analysis technique as its advantage of molecular fingerprint, ultra-sensitivity and non-contact. It is the most popular and easiest method to create SERS metal nanoparticles (NPs) combining magnetron sputtering deposition of noble metal with rapid annealing. In this study, we have demonstrated an approach to improve the SERS effect by using graphene oxide (GO) Au NPs composite structure. Here, we obtain the Au NPs coated SOI substrate prepared by magnetron sputtering 4 nm Au film and followed by rapid annealing treatment. The experimental results indicate that the SERS intensity is maximum of the Au NPs coated SOI substrate with the average particle diameter of 20 nm when the rapid annealing time is 30s and temperature is 500 degrees. Then, graphene oxide solution is spin coated on the Au NPs to form the GO-Au NPs composite structure. The morphology of GO-Au NPs have been characterized by scanning electron microscope (SEM). Rhodamine 6G (R6G) is used as the probe molecule to detect the SERS intensity. The GO-Au NPs has an excellent SERS effect which can detect R6G as low as 10^-9M. Besides, compared to the Au NPs without GO the GO-Au NPs has two times Raman intensity enhancement of bands at 774 cm^-1 because of the GO improving the SERS properties through strong ability of adsorption the probe molecule and chemical enhancement effect. Therefore, the GO-Au NPs composite structure shows a promising future to detect low concentration material.

Ag/Sn quasi-core/shell nanoparticles have been synthesized by a two-step reduction process at room temperature. The hybridization of elementary plasmons of Ag was detected by the photoluminescence spectra. In addition, the fluorescence quenching effect can be attributed to the strong interaction between Sn and Ag.

Recently, plasmonic quantum effects have become appreciated for its significant influence on surface plasmons coupling as the gapwidths down to sub-nanometer scale. In this paper, we assemble gold dimer structures with the gapwidths ranging from tens of to sub-nanometer scale by capillary force during solvent evaporation. It is found that surface plasmons coupling has translated from classical to quantum regime as the gapwidths down to sub-nanometer range. Emitting-polarization resolved scattering on these gold dimers is also performed. Different from the incident-polarization dependence, these emitting-polarization spectra can unveil the intrinsic antenna interactions between unpolarized illumination and surface plasmons modes. Furthermore, the polarization-resolved scattering spectra show that the quantum effects can influence the polarizability of antenna emission. These findings would be beneficial for the development of quantum plasmonic antenna and sensor designs, etc.

Eigenstates of Maxwell’s equations in the quasistatic regime were used recently to calculate the response of a Veselago Lens¹ to the field produced by a time dependent point electric charge.^{2, 3} More recently, this approach was extended to calculate the non-quasistatic response of such a lens. This necessitated a calculation of the eigenstates of the full Maxwell equations in a flat slab structure where the electric permittivity ϵ₁ of the slab differs from the electric permittivity ϵ₂ of its surroundings while the magnetic permeability is equal to 1 everywhere.⁴ These eigenstates were used to calculate the response of a Veselago Lens to an oscillating point electric dipole source of electromagnetic (EM) waves. A result of these calculations was that, although images with subwavelength resolution are achievable, as first predicted by John Pendry,⁵ those images appear not at the points predicted by geometric optics. They appear, instead, at points which lie upon the slab surfaces. This is strongly connected to the fact that when ϵ₁/ϵ₂ = −1 a strong singularity occurs in Maxwell’s equations: This value of ϵ₁/ϵ₂ is a mathemetical accumulation point for the EM eigenvalues.⁶ Unfortunately, many physicists are unaware of this crucial mathematical property of Maxwell’s equations. In this article we describe how the non-quasistatic eigenstates of Maxwell’s equations in a composite microstructure can be calculated for general two-constituent microstructures, where both ϵ and μ have different values in the two constituents.

The phenomenon of plasmon-induced transparency (PIT) is realized in surface plasmon polariton waveguide at the visible and near-infrared ranges. By adding one and two resonant cavities, the PIT peak(s) was (were) achieved due to destructive interference between the side-coupled rectangle cavity and the bus waveguide. The proposed structures were demonstrated by the finite element method. The simulation results showed that for three rectangle resonators system, not only can we manipulate each single PIT window, but also the double PIT windows simultaneously by adjusting one of the geometrical parameters of the system; for four rectangle resonators system, by changing the widths, the lengths and the refractive index of three cavities simultaneously, we would realize treble PIT peaks and induce an off-to-on PIT optical response. Our novel plasmonic structures and the findings pave the way for new design and engineering of highly integrated optical circuit such as nanoscale optical switching, nanosensor and wavelength-selecting nanostructure.

The mechanism of resonant perfect optical absorber (POA) is revealed by coupled mode method. The POA structures here is an air/grating/film/air four region asymmetric structures. Different with common POA structures that require metal film at the bottom to block the transmission of light, the film in our structures serves as a total internal reflection layer which blocks the transmission of light. To demonstrate that, mode dispersion analyses are provided for each mode by the phase plots of the scattering coefficients on each interface. The sufficient and necessary conditions of perfect optical absorption are derived from the phase matching conditions. Three analytical formulae are given for prompt and accurate design rules when the incident wavelength is slightly larger than the periodicity. Several fabrication schemes are discussed. The features of ultrathin structures, widely tunable POA wavelength, and high Q factor make our structures promising for applications in coherent thermal emission, filtering, sensing and modulation.

We report the direct imaging of plasmon on the tips of nano-prisms in a bowtie structure excited by 7 fs laser pulses and probing of ultrafast plasmon dynamics by combining the pump-probe technology with three-photon photoemission electron microscopy. A series of images of the evolution of local surface plasmon modes on different tips of the bowtie are obtained by the time-resolved three-photon photoemission electron microscopy, and the result discloses that plasmon excitation is dominated by the interference of the pump and probe pulses within the first 13 fs of the delay time, and thereafter the individual plasmon starts to oscillate on its own characteristic resonant frequencies. On the other hand, control of the near-field distribution was realized by variation of the phase delay of two orthogonally polarized 200fs laser pulses. The experimental results of the optical near-field distribution control are well reproduced by finite-difference time-domain simulations and understood by linear combination of electric charge distribution of the bowtie by s- and p- polarized light illumination. In addition, an independent shift of the excitation position or the phase of the near-field can be realized by coherent control of two orthogonally polarized fs laser pulses.

A circular slit-groove surface plasmon polaritons (SPPs) launcher surrounding a photodetector is employed theoretically to enhance the photocurrent of a typical Si-Ge photodetectors operating at telecommunication frequency regime. The slit and grooves are designed such that the SPPs are focused at the center of the absorption layer of the photodetector to result in additional electric current. Phase difference approach is applied to lead constructive interference between the incident light impinging from the top and the SPPs propagating toward the photodetector. Simulation result proves the interference and periodic behavior is observed. Finally the period of the groove, slit-groove distance, and slitphotodetector distance is determined via simulation. Furthermore it was shown that photocurrent increases by approximately 13-fold when the SPPs are introduced.

The development of plasmonic devices for sensing applications can offer high sensitivity and a dramatic improvement to the detection limits due to the high field enhancement at the metal surfaces. The platform proposed here is a tapered hybrid microfiber comprising a metal core and a glass cladding. The existence of a glass cladding not only serves as a mechanical host for the metal core, but also provides ease of handling regarding the tapering process. The advantages of this composite material system over pure metal tips are the absence of impurities and the multiple excitation of the plasmon modes due to the total internal reflection at the glass/air interface. The improved field enhancement at the apex of these tapered microwires was calculated through Finite Element Method (FEM) simulations. Enhancement factors up to 10⁴ were theoretically observed for this type of tapered microwires. The use of different metals having different melting points and thermal expansion coefficients as well as different glass thicknesses can lead to an optimization of the tapering process conditions in order to achieve tapered microwires with the desirable geometrical characteristics.

The interactions between surface plasmons in metal nanostructures and excitons in quantum emitters lead to many interesting phenomena that are strongly dependent on the quantum yield of surface plasmons. The experimental measurement of this quantum yield is hindered due to the difficulty in distinguishing all the possible exciton recombination channels. By utilizing the propagation of surface plasmons, we experimentally measured the decay rates of all exciton recombination channels, and thus obtained the quantum yield of single surface plasmons generated by a quantum dot coupled with a silver nanowire.

In this paper, superlens imaging with surface plasmon polariton cavities in both object and image space is proposed and investigated. A silver layer is added to an object mask to form a surface plasmon polariton (SPP) cavity in object space, which helps to greatly enhance evanescent waves generated by objects. As a result, better object imaging contrast can be obtained when compared with the single surface plasmon polariton cavity in image space only by amplifying the higher frequency componments while suppressing the long range plasmon mode. This is confirmed by the electric field distributions and optical transfer function of the system. The physical mechanism of the imaging quality improvements based on surface-plasmon polaritons is discussed. Finite-difference time-domain analysis method is used in the simulation.

We propose an ultra-compact graphene-based plasmonic modulation that is compatible with complementary metaloxide- semiconductor processing. The proposed structure uses a monolayer graphene as a mid-infrared surface waveguide, whose optical response is spatially modulated using electric fields to form a Fabry-Perot cavity. By varying the voltage acting on the cavity, the transmitted wavelength of the device could be controled at room temperature. The finite element method (FEM) has been employed to verify our designs. This design has potential applications in the graphene-based silicon optoelectronic devices as it offers new possibilities for developing new ultra-compact spectrometers and low-cost hyperspectral imaging sensors in mid-infrared region.

Due to the effect of plasmonic coupling, gold nanoparticle dimers have been paid more attentions in bio-imaging. The coupling effect existing at the gap between a closely linked particle pair can make the local field strongly enhanced and in which the angle between the excitation polarization and the dimer axis plays a dominant role. We calculated the amplitude distribution under a highly focused illumination objective. The simulation results show that for such a model, 45 degrees between the excitation polarization and the dimer axis can produce an optimum signal. The enhancement thus obtained is ~10.78 fold while the variation between peak-peak can reach 6.59 fold compared to a single plasmoic particle during the rotation of the polarization.

It is well known that when total internal reflection occurs at the interface between high to low refractive index, evanescent field will go into the media with low refractive index. This field can be scattered by a small dielectric particle on the surface. In this paper, with the aim to enhance the scattering field we introduced a thin gold film, the filed modified by the metallic film was theoretically calculated by FDTD solver. Further a polystyrene bead at the diameter of 200nm and 800nm was employed to test the model. Theoretical and experimental results agree well with each other that the locally excitated surface plasmon play a dominant role in the field enhancement scattered by the sphere.

The hybrid rib-slot-rib surface plasmon waveguide where a combined rib-slot-rib structure is added on the metal substrate within a low-index gap region with asymmetric structures is proposed using finite element method. Two types of asymmetric structures are introduced and their modal properties are discussed and compared to their traditional long range surface plasmon waveguide. Our designed structures can provide enhanced confinement energy within the gap region at proper parameters. Our simulation result is a guide for turning properties of plasmonic waveguide and providing ways for improved electromagnetic energy confinement in surface plasmon waveguide.

A novel and simple multi-wavelength band-pass filter based on metal-insular-metal (MIM) waveguide with different nanodisk cavity is proposed and investigated numerically by Finite-Element-Method (FEM) simulations. According to resonant theory of nanodisk, multi-wavelength band-pass filter can be achieved for different wavelength. It also shows that the transmission characteristics of the filter and the resonant wavelength can be easily manipulated by changing the gap between nanodisk and straight waveguide or changing the radius of the nanodisk. This kind of plasmonic waveguide filter may become important promising application in highly plasmonic integrated circuits.

Owing to the advantages of natural abundance, low cost, and amenability to manufacturing processes, aluminum has recently been recognized as a highly promising plasmonic material that attracts extensive research interest. Here, we propose a cavity-enhanced ultra-thin plasmonic resonator for surface enhanced infrared absorption spectroscopy. The considered resonator consists of a patterned ultra-thin aluminum grating strips, a dielectric spacer layer and a reflective layer. In such structure, the resonance absorption is enhanced by the cavity formed between the patterned aluminum strips and the reflective layer. It is demonstrated that the spectral features of the resonator can be tuned by adjusting the structural parameters. Furthermore, in order to achieve a deep and broad spectral line shape, the spacer layer thickness should be properly designed to realize the simultaneous resonances for the electric and the magnetic excitations. The enhanced infrared absorption characteristics can be used for infrared sensing of the environment. When the resonator is covered with a molecular layer, the resonator can be used as a surface enhanced infrared absorption substrate to enhance the absorption signal of the molecules. A high enhanced factor of 1.15×10⁵ can be achieved when the resonance wavelength of resonator is adjusted to match the desired vibrational mode of the molecules. Such a cavity-enhanced plasmonic resonator, which is easy for practical fabrication, is expected to have potential applications for infrared sensing with high-performance.

Raman spectroscopy provides intrinsic vibrational and rotational mode of molecules in materials, which is widely used in chemical, medical and environmental domains. As known, the magnitude of surface enhanced Raman scattering can be amplified several orders. Nowadays, common Raman scattering has been gradually replaced by surface enhanced Raman scattering in low concentration detection domain. Generally speaking, the signal of surface enhanced Raman scattering on periodic nanostructures is more reliable and reproducible than on irregular nanostructures. In this paper, two-dimensional gratings coated by noble metal are used as SERS-active substrate. The surface plasmon resonance can be obtained by tuning the period of two-dimensional grating when the excitation laser interacts on the grating. The local electric field distribution is simulated by finite-difference-time-domain (FDTD). The wavelength of 632.8nm and 785nm are usually assembled on commercial Raman spectrometer. The optimization procedure of two-dimensional grating period is simulated by FDTD for above two wavelengths. The relation between the grating period and surface plasmon resonance is obtained in theory. The parameters such as depth of photoresist and thickness of coated metal are systematic discussed. The simulation results will greatly guide our post manufacture, which can be served for the commercial Raman spectrometer in SERS detection.

Chirality is a highly important topic in modern chemistry, given the dramatically different pharmacological effects that enantiomers can have on the body. Chirality of natural molecules can be controlled by reconfiguration of molecular structures through external stimuli. Despite the rapid progress in plasmonics, active regulation of plasmonic chirality, particularly in the visible spectral range, still faces significant challenges. In this Letter, we demonstrate a new class of hybrid plasmonic metamolecules composed of magnesium and gold nanoparticles. The plasmonic chirality from such plasmonic metamolecules can be dynamically controlled by hydrogen in real time without introducing macroscopic structural reconfiguration. We experimentally investigate the switching dynamics of the hydrogen-regulated chiroptical response in the visible spectral range using circular dichroism spectroscopy. In addition, energy dispersive X-ray spectroscopy is used to examine the morphology changes of the magnesium particles through hydrogenation and dehydrogenation processes. Our study can enable plasmonic chiral platforms for a variety of gas detection schemes by exploiting the high sensitivity of circular dichroism spectroscopy.

We proposed a symmetric V-type slit array to tune the propagation direction of surface plasmon polaritons by external control of the polarization and/or the inclination angle of the incident light. Using theoretical analysis and numerical simulation, we studied the position-related phase and spin-related phase of the SPPs excited by an inclined and circularly polarized light through a column of slits to determine the parameter of the structure. The results showed that we can tune the propagation of the SPPs with significant flexibility, by changing the polarization of the incident light and the inclination angle of the incident light. Furthermore, a nanostructures were designed to control directional launching of surface plasmons based on the principle of optical spin’s effect for the geometric phase of light. The propagation direction of the generated SPPs can be controlled by the spin of photons. The total size of the surface plasmon polariton (SPP) launcher is 320 nm by 180 nm, which is far smaller than the wavelength of the incident light. This result may provide a new way of spin-controlled directional launching of SPP.