This PDF file contains the front matter associated with SPIE Proceedings Volume 10722, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

The prospect of ultrasensitive, rapid, and cost-effective molecular analysis has been one of the main drivers behind the rapidly evolving field of plasmonics. I will illustrate this development by describing several recent molecular sensing and actuation experiments that are all based on the extremely efficient conversion of light from the far-field to or from the near-field by virtue of plasmon excitation in metal nanostructures. The examples utilize different kinds of molecular contrast (fluorescence, Raman scattering, refractive index, viscosity) as well as plasmon-enhanced thermal and optical forces for diverse applications, including controlled DNA release, detection of nerve gases, and studies of molecular interactions at the single molecule limit.

As a result of recent developments in nanofabrication techniques, the dimensions of metallic building blocks of plasmonic devices continue to shrink down to nanometer range thicknesses. The strong spatial confinement in atomically thin films is expected to lead to quantum and nonlocal effects, making ultra-thin films an ideal material platform to study light-matter interactions at the nanoscale. Most importantly, the optical and electronic properties of ultra-thin plasmonic films are expected to have a strong dependence on the film thickness, composition, strain, and local dielectric environment, as well as an increased sensitivity to external optical and electrical perturbations. Consequently, unlike their bulk counterparts which have properties that are challenging to tailor, the optical responses of atomically thin plasmonic materials can be engineered by precise control of their thickness, composition, and the electronic and structural properties of the substrate and superstrate. This unique tailorability establishes ultra-thin plasmonic films as an attractive material for the design of tailorable and dynamically switchable metasurfaces. While continuous ultra-thin films are very challenging to grow with noble metals, the epitaxial growth of TiN on lattice matched substrates such as MgO allows for the growth of smooth, continuous films down to 2 nm. In this study, we present both a theoretical and an experimental study of the dielectric function of ultrathin TiN films of varying thicknesses. The investigated ultrathin films remain highly metallic, with a carrier concentration on the order of 1022 /cm3 even in the thinnest film. Additionally, we demonstrate that the optical response can be engineered by controlling the thickness, strain, and oxidation. The observed plasmonic properties in combination with confinement effects introduce the potential of ultra-thin TiN films as a material platform for tailorable plasmonic metasurfaces.

In bioanalysis, especially in single cell analysis, label-free detections and recognitions for molecular analysis are highly demanded. IR spectroscopy is one of label-free methods and it gives us chemical specificity and molecular information, yet its application in bioanalysis is limited due to its low sensitivity. Recently, plasmonic nanostructures were intensively studied to improve the sensitivity of IR spectroscopy by several orders of magnitude, however positioning analytes exactly at the hot-spots is still challenging. We propose a device that utilizes nanofluidics to manipulate analytes into the hot-spots of metamaterials, consequently an ultra-high sensitivity of IR absorption detection can be achieved. The structure consists of metal square-disks array and metal mirror separated by a nano fluidic channel. The interaction between top square nanostructure and bottom mirror forms the quadrupole resonance, and it suppresses the light reflection from the device. When the molecule whose absorption is overlapped with this mode is introduced, strong interaction between molecules and metamterials is excited and it creates the reflection light within the absorption band of the metamaterial. The sensitivity was achieved at molecule density of ~10^-4 molecules/Å^2, which is improved by 2 orders compared to reported plasmonic induced IR detection methods. We also succeeded in the quantitative determination of absolute number of molecules by precise fluidic operation. Moreover, the device allows the confinement of both molecules and plasmonic energy inside the nanocavities. We confirmed the presence of a strong H-bond network and the scaling behavior of water confined in 10-100 nm regime. Our method can provide the capability for in-situ probing molecules and chemical reactions under nanoconfinement.

In the recent decade two-dimensional transition metal dichalcogenides (2D TMDs) has attracted great attention in a variety of optoelectronic applications including photodetectors, optical chemical sensors, light-emitting diodes, lasers, and opto-valleytronic devises because of their high ON/OFF current ratios, low sub-threshold switching, strong photoluminescence, controllable valley polarization and high thermal stability. Despite their excellent optoelectronic properties, their optoelectronic applications are limited by the weak light-matter interaction in 2D TMDs due to the atomic thickness. Because plasmonic metal nanoparticles (NPs) have the capability to concentrate light beyond the diffraction limit, there is an emerging trend of exploiting light-matter interactions in hybrid systems consisting of 2D TMDs and plasmonic metal NPs for boosting the performance of 2D TMD-based optoelectronic devices. Plasmonic metal NPs have been employed to enhance light-matter interactions in quantum emitters including dye molecules and quantum dots through mechanisms such as Fano interference, strong coupling, plasmon-induced resonance energy transfer, and plasmon-enhanced emission. However the understanding and the active control of the interaction between 2D TMD and plasmonic NPs are still limited. So, herein, we report two tunable plasmon-exciton interactions that are novel in hybridized systems consist of 2D TMD and plasmonic NPs: (1) tunable plasmon-induced resonance energy transfer from a single Au nanotriangle (AuNT) to monolayer MoS2; (2) tunable Fano resonance and plasmon-exciton coupling in a single AuNT on monolayer WS2 at room temperature. In the first case, we report the first observation and tuning of plasmon-trion and plasmon-exciton resonance energy transfer (RET) from a single AuNT to monolayer MoS2 at room temperature. We achieved these phenomena by the combination of rational design of hybrid 2D TMD-plasmonic NP systems and single-nanoparticle measurements. By combining experimental measurements with theoretical calculations, we conclude that the efficient RET between SPs of metal NPs and excitons or trions in monolayer MoS2 is enabled by the large quantum confinement and reduced dielectric screening in monolayer MoS2. In the second case, we report tunable Fano resonances and plasmon-exciton coupling in 2D WS2-AuNT hybrids at room temperature. The tuning of Fano resonances and plasmon-exciton coupling was achieved by active control of the WS2 exciton binding energy and dipole-dipole interaction through controlling the dielectric constant of the surround medium. Specially, Fano resonances are controlled by the exciton binding energy or the localized surface plasmon resonance (LSPR) strength through tuning the dielectric constant of surrounding solvents or the dimension of AuNTs. Additionally, we observe a transition from weak to strong plasmon-exciton coupling when increasing the dielectric constant of surrounding solvents. Large coupling strength of 80-100 meV is obtained at room temperature due to the strong field localization of the AuNTs and large transition dipole moment of the WS2 exciton. Our results provide guidance on systematic tuning of the Fano line-shape and Rabi splitting energies at room temperature for 2D TMD-plasmonic NP hybrids.

In the last decade, nanotechnologies and biomedicine have reached remarkable levels of integration and cross-fertilization aiming to address unmet clinical needs by designing functional materials and transformative technologies for precision medicine. This seminar will review how we harness light-matter interaction at the nanoscale to design artificial materials with fascinating properties mainly originating by form-function relationships. Among several others, hybrid nano-carriers, viral cargos, plasmonic metamaterials represent only a small fraction of a large variety of systems proposed to achieve local drug-delivery, photo-thermal and photodynamic therapies, high resolution imaging and sensing, stimulated specific immune response to treat and monitor neurodegenerative diseases and cancers. In this context, we have developed miniaturized plasmonic biosensor platforms that outperform current sensing technologies and are based on hyperbolic metamaterials which support highly confined bulk plasmon modes. Recent opto-genetic research activities based on neurophotonics approaches will be discussed. This research is a major scientific and technological challenge that will revolutionize our capability of managing and exploiting neuronal circuits.

We propose a metamaterial perfect absorber (MPA) solar cell to utilize the light confinement effect of MPA and to enhance the light absorption of the cell. The MPA consists of two distinct metallic structures sandwiching a thin dielectric layer as a spacer. Under light irradiation, a magnetic resonance mode is excited in the MPA at a certain wavelength, leading to light confinement in the dielectric thin layer. We propose to replace the dielectric layer with the photoelectric conversion layer of an organic thin-film solar cell (OSC), so as to confine the light into the layer, leading to light absorption enhancement without changing the layer thickness. In this research, we introduced metallic nanostructures into a solar cell device to form the metamaterial perfect absorber configuration, and examined the light absorption enhancement of the cell. A periodic Ag nanostripe array was fabricated on a transparent electrode. Thin films of zinc oxide, poly (3-hexylthiophene): [6, 6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM), molybdenum oxide, and aluminum were laminated on the Ag nanostripes so as to make a solar cell. Reflection spectra were measured with light incident from the glass side of the MPA solar cell. The relative extinction is the ratio of the extinction spectra of OSCs with and without Ag nanostripes were calculated. The average extinction ratio in the absorption wavelength range of the P3HT:PC61BM layer was 1.18, suggesting the MPA configuration confined sunlight into the P3HT:PC61BM layer, leading the light absorption increase of the layer by a factor of 18%.

The growing field of quantum plasmonics lies at the intersection between nanophotonics and quantum optics. QUantum plasmonics investigate the quantum properties of single surface plasmons, trying to reproduce fundamental and landmark quantum optics experiment that would benefit from the light-confinement properties of nanophotonic systems, thus paving the way towards the design of basic components dedicated to quantum experiments with sizes inferior to the diffraction limit. Several groups have recently reproduced fundamental quantum optics experiments with single surface plasmons polaritons (SPPs). We have investigated two situations of quantum interference of single SPPs on lossy beamsplitters : a plasmonic version of the Hong-Ou-Mandel experiment, and the observation of plasmonic N00N states interferences. We numerically designed and fabricated several beamsplitters that reveal new quantum interference scenarios, such as the coalescence and the anti-coalescence of SPPs, or quantum non-linear absorption. Our work show that losses can be seen as a new degree of freedom in the design of plasmonic devices.

Quantum effects play a significant role in nanometric plasmonic devices, such as small metal clusters and metallic nanoshells. For structures containing a large number of electrons, ab-initio methods such as the time-dependent density functional theory (TD-DFT) are often impractical because of severe computational constraints. Quantum hydrodynamics (QHD) offers a valuable alternative by representing the electron population as a continuous fluid medium evolving under the action of the self-consistent and external fields. Although relatively simple, QHD can incorporate quantum and nonlinear effects, nonlocal effects such as the electron spillout, as well as exchange and correlations. Here, we show an application of the QHD methods to the plasmonic breathing oscillations in metallic nanoshells. We illustrate the main advantages of this approach by comparing systematically the QHD results with those obtained with a TD-DFT code.

Surface Plasmons has been recognized as a promising platform that premises the advance of diverse optoelectronic materials and devices. Very recently it is noted that the potential of plasmonics is rapidly extended to wider scientific areas. In this presentation, we introduce our recent efforts to utilize plasmonics for versatile applications and understand its fundamental nature. Plasmonic effects have been proposed as a solution to overcome the limited light absorption of thin film photovoltaic devices and diverse types of plasmonic solar cells have been developed. We demonstrate a viable and promising optical engineering technique enabling the development of high-performance plasmonic organic photovoltaic devices. Laser interference lithography was explored to fabricate metal nanodot (MND) arrays with elaborately controlled dot size as well as periodicity. MND arrays with ~91 nm dot size and ~202 nm periodicity embedded in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) hole transport layer remarkably enhanced the average power conversion efficiency (PCE) from 7.52% up to 10.11%, representing one of the highest PCE and degree of enhancement (~34.4%) levels compared to the pristine device among plasmonic OPVs reported to date. The development of highly sensitive and selective photodectors has been an interesting issue yet to be resolved, for which we introduce a simple protocol for the fabrication of wavelength-selective photodiodes or high-gain photoconductors at low voltage. Herein, size-controlled silver nanoparticles (AgNPs), gold nanoparticles (AuNPs) and gold nanorods (AuNRs) have been introduced into polymer photodiodes. The evaluated devices exhibit remarkable photocurrent enhancement at corresponding plasmon resonant wavelengths, directly resulting in the photosensitivity increase. When compared with a pristine photodiode, AgNPs-, AuNPs- and AuNRs-mediated devices unveil maximum enhancement of 46, 49 and 65% for responsivity and 39, 30 and 54% for detectivity for blue (450 nm), green (525 nm) and red (620 nm) light detection, respectively. We also integrated a uniformly-distributed layer of Au nanorods (AuNRs) into vertically-structured perovskite photoconductive photodetectors and report, as a result, perovskite-AuNR hybrid photodetectors that exhibit significant photocurrent enhancements. The high responsivity and low driving voltage place this device among the highest-performing perovskite-based thin-film photoconductive photodetectors reported. Unique features can be observed if the characteristics of the light emitters and metal nanoparticles are integrated. Photoluminescence (PL) can be enhanced or quenched by the presence of neighboring plasmonic metal nanostructures. An unambiguous study of the mechanism behind the enhancement and the quenching of emission is necessary to obtain new insight to the interaction between light and metal-fluorophore nanocomposites. The core aspect of combining plasmonic metal nanostructures with fluorophores is discussed by considering various functional roles of plasmonic metals in modifying the PL property. A few representative applications of SPR mediated luminescence are also discussed. We demonstrate the surface-plasmon-induced enhancement of Förster resonance energy transfer using a model multilayer core-shell nanostructure consisting of an Au core and surrounding FRET pairs, i.e., CdSe quantum dot donors and S101 dye acceptors. The multilayer configuration was demonstrated to exhibit synergistic effects of surface plasmon energy transfer from the metal to the CdSe and plasmon-enhanced FRET from the quantum dots to the dye. With precise control over the distance between the components in the nanostructure, significant improvement in the emission of CdSe was achieved by combined resonance energy transfer and near-field enhancement by the metal, as well as subsequent improvement in the emission of dye induced by the enhanced emission of CdSe. Consequently, the Förster radius was increased to 7.92 nm and the FRET efficiency was improved to 86.57% in the tailored plasmonic FRET nanostructure compared to the conventional FRET system (22.46%) without plasmonic metals. Metal-free purely organic phosphorescent molecules are attractive alternatives to organometallic and inorganic counterparts because of their low cost and readily tunable optical properties through a wide chemical design window. However, their weak phosphorescent intensity due to inefficient spin-orbit coupling and consequently prevailing non-radiative decay processes limits their practical applicability. Here, we systematically studied phosphorescence emission enhancement of a purely organic phosphor system via plasmon resonance energy transfer. By precisely tuning the distance between purely organic phosphor crystals and plasmonic nanostructures using layer-by-layer assembled polyelectrolyte multilayers as a dielectric spacer, maximum 2.8 and 2.5 times enhancement in photoluminescence intensity was observed when the phosphor crystals were coupled with ~55 nm AuNPs and ~7 nm AgNPs, respectively, at the distance of 9.6 nm. When the distance is within the range of 3 nm, a dramatic decrease in phosphorescence intensity was observed while at a larger distance the plasmonic effect diminished rapidly. The distance-dependent plasmon-induced phosphorescence enhancement mechanism was further investigated by time-resolved photoluminescence measurements. Our results reveal the correlation between the amplification efficiency and plasmonic band, spatial factor, and spectral characteristics of the purely organic phosphor, which may provide an insightful picture to extend the utility of organic phosphors by using surface plasmon-induced emission enhancement scheme. Surface plasmon based optical biosensors constitute a well-established model that efficiently realized the activity of plasmonics for viable optoelectronics. A massive amount of approaches was demonstrated to enhance the sensitivity via combined localized and propagating modes, and more recently an increasing attention has been paid to graphene plasmons. Hybrid plasmonic nanostructures comprising gold nanoparticle (AuNP) arrays separated from Au substrate through a temperature-sensitive poly(N-isopropylacrylamide) (PNIPAM) linker layer were constructed, and a unique plasmonic-coupling-based surface plasmon resonance (SPR) sensing properties was investigated. We also investigated for the first time the dependence of the coupling behavior in AuNPs with controlled density on the temperature in a quantitative manner in terms of the change in SPR signals. The device containing AuNPs with optimized AuNP density showed 3.2-times enhanced sensitivity compared with the control Au film-PNIPAM sample. The refractive index sensing performance of the Au film-PNIPAM-AuNPs was greater than that of Au film-PNIPAM by 19% when the PNIPAM chains have a collapsed conformation above LCST. The use of graphene in conventional plasmonic devices was suggested by several theoretic researches. However, the existing theoretic studies are not consistent one another and the experimental studies are still at the initial stage. In order to reveal the role of graphenes on the plasmonic sensors, graphene oxide (GO) and reduced graphene oxide (rGO) thin films were deposited on Au films and their refractive index (RI) sensitivity was compared for the first time in SPR-based sensors. The deposition of GO bilayers with number of deposition L from 1 to5 was carried out by alternative dipping of Au substrate in positively- and negatively-charged GO solutions. The fabrication of layer-by-layer self-assembly of the graphene films was monitored in terms of the SPR angle shift. GO-deposited Au film was treated with hydrazine to reduce the GO. For the rGO-Au sample, 1 bilayer sample showed a higher RI sensitivity than bare Au film, whereas increasing the rGO film from 2 to 5 layers reduced the RI sensitivity. In case of GO-deposited Au film, the 3 bilayer sample showed the highest sensitivity. The biomolecular sensing was also performed for the graphene multilayer systems using BSA and anti-BSA antibody. We also suggest a paradigm to better understand the mechanism of the enhanced performance of coupled graphene and surface plasmon based sensors in terms of surface potential and work function. Plasmon metal nanoparticles can induce an improvement of the catalytic efficiency of rationally designed composite catalysts. Despite efforts to combine the plasmonic effect and the catalytic fingerprints in metal-based catalytic systems, corresponding mechanistic studies based on electrochemical methods have remained challenging to date. In this context, the transition from plasmon metals to catalytic metals based core-shell heterostructures in plasmonic photo-electrocatalysis provides a sustainable route to high-value catalytic activity and confirm the practical potential of plasmon-mediated electrocatalytic performance. Here we report an enhancement of the catalytic activity toward an improved generation of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) on Au nanoparticles (AuNPs) using visible light. Materials characterization and enhanced catalytic activity of both H2 and O2 generation using visible light inferred the advantageous incorporation of rGO with tuned layer thickness. This model system allows us to decisively separate the optical and catalytic function of the hybrid nanomaterial and determine that the flow of energy is strongly biased towards the excitation of energetic charge carriers in the Pd shell. For photo-electrocatalytic properties of AuNP@rGO@Pd nanostructures during reaction, in-situ observation was utilized to advance our understanding of the fundamental physical and chemical properties of high-performance. Lastly, we introduce an unprecedented strategy to rationally quantify the plasmonic effects on electro-/-photo-catalysis using modified Kreschmann setup and KPFM study.

The mechanism of supperresolution found in dielectric microlenses has been a puzzle for a long time. Many proposals or models have been put forward but the underlying mechanism still remains unclear. Here we experimentally demonstrate that, when lifting a microlens above a sample, the defocused images taken by the microlens behave like those of conventional lenses, thus excluding evanescent waves as a likely mechanism for superresolution. We further employ a heating method to scan across optical resonant conditions of a microsphere while simultaneously monitoring the image resolution. The null result also excludes photonic nanojets to be the mechanism for superresolution. We also find the microlenses exhibit an interesting diameter-dependent resolving power, indicating effects beyond ray optics. Finally, we discover that the superresolution is mainly achieved by coherent imaging, assisted by surface plasmons of the underneath samples.

MicroLED display is emerging as a candidate to drive a new generation of display technology. Full-color microLED based on carbon-dots (CDs) and blue microLED utilizes photoluminescence (PL) of blue-excited red and green emission CDs to achieve large coverage of color gamut and low power consumption. There is a high demand to develop costeffective technologies to enhance CD emission and minimize blue excitation light leakage through the CD layer. Here we demonstrate the use of plasmonic nanoparticles to enhance multicolor CDs in the emitting layer of microLED while suppressing the transmission of blue excitation. Silver nanoparticles are known to have surface plasmon resonances in or close to the blue range. Blue excitation over an emitting layer formed by the mixture of CDs and metal nanoparticles leads to excitation enhancement of CDs and thus the increased quantum efficiency. We studied the emitting layers fabricated by dispersing a mixture of 30 nm silver nanoparticles and CDs at various ratios and obtained a maximum enhancement factor of ~8. The metal nanoparticles also absorbed the blue excitation and reduced the leakage of blue light. Fluorescence lifetime measurements showed negligible changes in the CD emission rate with and without the presence of metal nanoparticles. The analysis implies that the enhanced CD PL is a result of excitation enhancement rather than Purcell effect. This technique offers a low-cost, effective approach to improve the performance of microLED displays.

Recently, various surface plasmon polariton (SPP) resonator structures with a tiny volume and a sharp resonance are numerically proposed for sensor, filter and modulator integrated devices. However, there are few experimental demonstrations of such the structure, i.e., a combination of SPP resonator and SPP waveguide, in the range from visible to telecommunication wavelength. We will present several tiny SPP resonator devices with SPP I/O ports, i.e., a combination of SPP resonator with a volume of less than 1 squared micrometer and a channel-type SPP waveguide with a width of 200 nm width. We have fabricated such the resonators for integrated applications by using EB lithography technique and evaluated their optical resonance characteristics for a refractive index sensor in the telecommunication wavelength region. And we will discuss key points to achieve enough performance as integrated functional devices for real applications.

As a powerful and compact device for manipulating wavefront of light, metasurface has widely been studied in recent years. However, simultaneous control of full parameters of light (including amplitude, phase, and polarization) over a wide bandwidth is still a great challenge. In our works, we demonstrate that the combination of subwavelength plasmonic structures and detour phase could achieve full parameter control of light. Here, the traditional detour phase is used to manipulate the phase of light, while several different plasmonic structures are designed to control the amplitude and various polarization state distributions. We first introduce a type of detour phase meta-hologram composed of cross-shaped plasmonic nano-silt array which are sensitive to linear polarization with over 1000-nm bandwidth from visible to near-infrared. In a proof-of-concept experiment, we demonstrate 3D object reconstruction and polarization multiplexing images at various prescribed wavelengths from 473 nm to 1550 nm using a specially designed meta-hologram. Then we introduce another design of detour phase meta-hologram which is sensitive to circular polarizations. We choose a pair of oblique plasmonic nano-slits as a unit cell in the hologram, and modulate its polarization response by changing the distance between the two slits in a unit cell. We demonstrate that such design can be used for detecting both topological charge and polarization order of vortex vector beam, or generating holographic patterns with RGB colors. Benefiting from high controllability of amplitude, phase, and polarization, our meta-holograms offer great potential in future applications such as 3D displays, optical communications, and beam shaping.

The investigation of light-matter interaction has had growing interest in the field of photonics. In particular, metalinsulator-metal (MIM) sensors are of interest owing to their high sensitivity compared to conventional sensor made by a single metal layer. The high resolution and low concentrations detection is a result of the sharp resonance of the surface plasmon polariton waveguide hybrid mode at the Au/water interface supported by MIM structures. In this context, we have implemented experiments and theoretical simulations to estimate the enhancement of the sensitivity of metal-insulatormetal sensors. By changing the refractive index of an aqueous solution of glucose, we found that the use of a metalinsulator-metal stack improves the figure of merit of the sensor 7.5 times compared to that of a conventional surface plasmon resonance sensor.

In this report, we introduce our proposed nanophotonic structures for highly efficient optical manipulation, including utilizing photonic crystal waveguides, nanocavities, and metallic structures with localized surface plasmon resonances. Owing to their waveguide-accessible configurations and highly concentrated optical modes with large field gradients beyond the diffraction limit, highly efficient optical trapping can be realized in sub-wavelength scale.

In nature, magnetic effects on materials are weaker than their electric counterparts. Magnetic polarizability is especially difficult to achieve at optical frequencies since natural materials are non-magnetic at this frequency range and magnetic effects can thus only be generated by carefully tailoring the spatial distribution of electric permittivity. Plasmonic nanostructures offer a flexible platform to engineer meta-atoms that satisfy such conditions and enhance the local magnetic field. However, thus far, this magnetic enhancement has always been accompanied with an enhancement of the electric response as well, such that pure magnetic modes were not yet observed in plasmonic systems. In this work, we design, fabricate and characterize a novel plasmonic nanostructure, which supports a pure magnetic dipole mode under plane wave excitation without contamination from electric modes. This study employs rigorous multipolar mode analysis and clearly distinguishes magnetic dipole and electric quadrupole effects. The link between structural asymmetry and multipole composition that is revealed in this work will be particularly useful in research on symmetry-sensitive physical phenomena, including optically induced atomic transition, optical forces, fluorescence, thermal emission and nonlinear optics.

An electron beam passing over metallic gratings can emit Smith-Purcell radiations (SPRs). The electron beam can also excite surface plasmons (SPs) on the metallic surface. Recently, the generation of convergent light beam by SP-manipulated SPRs on metallic chirped gratings has been explored. However, for the one-dimensional gratings, only the emission along the direction of gratings (i.e. the direction of electron beam) is convergent. Therefore, the emission pattern is a line instead of a spot. In this work, the electron beam passing through the arrays of Yagi-Uda nanoantenna for generation of convergent light spot based on SP-manipulated SPR is proposed and investigated by FDTD simulation. The convergent spots that are formed directly above the nanoantenna arrays with different wavelengths are demonstrated. The emission angles controlled by the structure parameters and electron beam energy are also examined. This work provides a way toward practical applications in the fields of optical imaging, holography, cryptography and tunable visible light source.

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.

The metasurface under study was engineered to enhance the local fields, which is crucial for the efficiency of the nonlinear photon conversion. In our design of the metasurface, we make use of high-Q collective resonances common to regular arrays of semiconductor particles, as verified by MIR FTIR spectroscopy. We facricate 600-nm-thick silicon rectangles situated on a sapphire substrate. In order to demonstrate power- dependent blue-shifting of THG, we focused a 200 ± 30 fs MIR laser pulses centered at λ = 3.62 μm, with a variable non-destructive fluence in the 1 < F < 6 mJ/cm2 range, onto the metasurface to achieve 5 < I < 30 GW/cm2 intensity. The advantage of operating in the MIR regime is that the refractive index change scales as ∆n(t) ∝ −N(t)λ^2, which is crucial for photon acceleration; here, N(t) is the time-dependent FC density. The concept of photon-acceleration-induced spectral shifting of the nonlinearly upconverted signal in a metasurface- based semiconductor cavity is as follows. MIR photons interact with, and get trapped by, the metasurface. As FCs are generated by four-photon absorption in silicon, the resonant frequency of the metasurface blue-shifts, and the frequency of the trapped photons follows. Accelerated MIR photons then upconvert via the standard χ(3) nonlinear process, resulting in the observed blue-shifting of the third harmonic generation (THG). As a result, the spectral peak and width of the THG light generated in the metasurface can be controlled by incident fluence. The central THG wavelength can be blue-shifted by more than 30 nm, enabling harmonics generation with center frequencies of up to ≈ 3.1ω. In contrast, the same measurements performed in unstructured silicon films yield no apparent spectral modifications to THG. A common belief is that the resonant enhancement of the THG must be accompanied by spectral narrowing; in contrast, here, due to photon acceleration, we observe spectral broadening of the resulting THG spectrum by approximately 50%. We connect the observed blue shift and broadening of the THG spectrum with the time-dependent nature of the complex eigenfrequency of the mode. Qualitative agreement is reached between the experimental data and the calculations based on a coupled mode theory with the eigenfrequency ωR(t) and damping factor γR(t) being driven by the pump pulse through free carrier generation. We find photon acceleration in semiconductor metasurfaces a promising tool for active control over the frequency of light in prospective nanophotonics devices.

Since its discovery in the 1960s, nonlinear optics has revolutionized optical technologies and laser industry. Development of efficient nanoscale nonlinear sources will pave the way for new applications in photonic circuitry, quantum optics and bio-sensing. However, nonlinear signal generation at dimensions smaller than the wavelength of light brings new challenges. These include the reduced light-matter interaction volume, mode overlap and increased losses. Here, we develop hybrid plasmonic – dielectric metamaterials that overcome these limitations and show a dramatic increase of the efficiency of nonlinear optical response at the nanoscale. In the first part of my talk I will introduce a new type of 3-dimensional, non-planar plasmonic metasurface and demonstrate 4 orders of magnitude enhancement of second harmonic generation (SHG) compared to doubly-resonant plasmonic systems. The geometry of the metamaterial design minimizes the destructive interference of nonlinear emission into the far-field, provides independently tunable resonances both for fundamental and harmonic frequencies, a good mutual overlap of the modes and a strong interaction with the nonlinear material. In the second part of my talk I will describe our recent efforts to combine localized plasmon modes with propagating photonic waveguide modes. The hybridized mode that is formed as a result of such coupling can exhibit the desirable features of plasmonic modes such as high Purcell factors and large field enhancement but with significantly reduced losses. Our findings can enable the development of efficient nanoscale single photon sources, integrated frequency converters and other nonlinear devices.

Increasing the nonlinear conversion efficiency of metals at the nanoscale often relies on the use of plasmonic near-field hot spots in metallic nanostructures with tiny gaps. However, such nanoscale gaps often quench the second-harmonic generation (SHG) due to the cancellation of surface dipoles, making it a challenge for efficient optical frequency-conversion and nonlinear nanoscopy enhancement at the deep-subwavelength scale. Here we demonstrate that the SHG silencing can be overcome in the sub-nanometer gap of a single plasmonic particle-on-film nanocavity, which exhibits a surprisingly larger SHG conversion efficiency up to 1.0×10^(-8) W-1. On the one hand, laser scanning confocal imaging of single particle-on-film nanostructures reveals unambiguously that the enhanced nonlinear optical emissions originate from resonant excitation of the gap plasmon, which amplifies the nonlinear source at the fundamental frequency. On the other hand, full-wave electromagnetic simulations uncover that the structural symmetry breaking in the plano-concave gap suppresses the cancellation of SH dipoles, which, together with the resonance excitation enhancement, renders the plasmonic nanocavity an extremely small yet bright nonlinear optical source for the development of next generation chip-scale photonic nanodevices.

A surface plasmonic wave device for biological sensing is demonstrated. It consists of one-dimensional PMMA grating on an aluminum layer. This plasmonic device could increase the fluorescence intensity once the direction of the above dielectric grating and the pumping light could fit to the momentum matching condition. Here we incorporate a spider silk film into such fabricated plasmonic device as an intermediate layer to bridge the inorganic device surface and biological systems of interest. Specifically, a biocompatible spider silk film is casted on the device, followed by further grating fabrication and biomolecular conjugation via enzymatic reactions. Here in the research, antibodies and other proteins are assembled on the fabricated layer of spider silk film specifically with retained activities upon the enhanced fluorescence detection. Unlike other fabrication processes that require material-dependent surface treatments prior to biomolecular conjugation, the additional spider silk film provides an alternative strategy for facile and selective biological assembly in the biosensor. This, we envision, renders an unprecedented advantage for fabricating biosensors with various settings regardless of structural configurations or the building materials of the devices. Overall, the intermediate layer fabricated with spider silk under such grating structures not only demonstrates the strong surface field to enhance the pumping efficiency, but also enables binding of many target biomolecules for sensing and detection.

When the size of metallic nanoparticles becomes smaller than 1 nm, of which nanostructures are composed of several tens of atoms, the plasmonic effect disappears and the electronic energy levels of the nanoparticles called as nanoclusters are quantized. Then, the nanoclusters can emit fluorescence of which wavelength depends on their size. We investigated synthetic method of Platinum nanoclusters (Pt NCs) that exhibit blue to yellow photoluminescence by a facile one-pot reduction method. They were synthesized from the mixture of H2PtCl6, hyper-branched polyethylenimine (PEI), and L-ascorbic acid, resulting in the formation stabilized with the amino groups in the cavities formed by coiled PEI ligands. The chain conformation of cationic polymer PEI depends on pH of solution. By controlling pH of the synthesis solution, the size of Pt NCs@PEI changes and their fluorescent wavelength can be tuned. Pt NCs@PEI were applied to the labeling of Chemokine receptors of the membrane of cancer HeLa cells and Glutamate receptors of the membrane of neural cells by binding them to an antibody via a conjugate protein for bio-imaging. They showed lower cell cytotoxicity than other nanoparticles such as Q-dots@COOH, indicating that they have better cell viability and great potential for biological applications.

Transition dichalcogenide monolayer (1L-TMD) such as MoS2, MoSe2, WS2 and WSe2 are promising 2D semiconductors with visible or near-IR wavelength emission, suitable for the nanophotonics applications including quantum optical emitters. 1L-TMDs offer advantages such as direct growth on wafers, the ability to tune the properties of the material by controlling the layer thickness, electrostatic doping, and hetero-stacking. Atomically thin, flat geometry of two-dimensional (2D) semiconductors provides the ideal coupling configuration between plasmons and excitons, leading to a new realm of light-matter interaction. It has been shown that the simple hybrid of placing Ag nanowires on MoS2 monolayers forms a highly efficient plasmon emitter and detector. Optoelectronic applications in two-dimensional (2D) transition-metal dichalcogenides (TMDs) are still limited by the weak light absorption, and moreover peak positions and shapes of exciton complexes are sensitively perturbed by varying excitation conditions, inherent from nature of atomically thin layers. Here we show that coupling of excitons with plasmons can spectrally refine the exciton emission of 1L-TMDs, maintaining contribution of only neutral excitons even with high excitation power.

We introduce preliminary work aiming at developing a new generation of bio-enabled nanoscopic antennas which relies on quantum coherence to transform light energy into collective electronic excitations. The idea of super-radiant coupling between plasmons and molecular excited states has been discussed before, theoretically, in simplified contexts, e.g two state systems, in absence of geometric spatial symmetry considerations. Symmetry of molecular electronic states, and mesoscopic geometric constraints are factors that for the time being are easier to tackle experimentally. In our experiments, we decorate the surface of an icosahedral virus protein cage with organic dyes which interact strongly with the virus surface via intermolecular forces. We study the fluorescence emission under ultrafast pumping, in terms of intensity and lifetime as we increase the number of chromophores per particle. We find that, the initial increase in the number of chromophore, is accompanied by concentration quenching as one would expect from a dense chromophore system near thermodynamic equilibrium. However, above a threshold value (N = 135, 75% coverage), the intensity of fluorescence emission suddenly increases several times. The fluorescence lifetime is shorter than what we could measure with the current setup. We believe this to be a strong indication that collective relaxation tends to dominate emission when reaching near complete coverages. Control experiments that perturb the shell-chromophore interaction also destroy the suppression of fluorescence quenching effect. To study the near-field energy transfer between the chromophores excited state and the surface plasmon of a metal nanoparticle we encapsulate the later into a chromophore studded virus protein shell. Preliminary results show that the ratio of the integrated spectral density of emission from virus-like particles containing metal to the spectral density of emission from free dye depends on pump power. The same ratio is independent of pump power in the nanoparticle absence.

Nanoantenna enhanced fluorescence is a promising method in many emergent applications such as single molecule detection. However, the excitation wavelengths and the emission wavelengths of emitters could be well-separated depending on their Stokes-shifts, preventing optimal fluorescence enhancement by a rudimental nanoantenna. Here we propose an Ag-Si hybrid stack nanoantenna, which comprises an Ag bottom cylinder and a Si top cylinder, to match the Stokes-shift of the fluorescence emitter. The Ag cylinder is designed to resonate at the excitation wavelength of the emitter, yielding a large field enhancement to boost the excitation rate of the emitter. Meanwhile, the resonance of the low loss Si cylinder is designed to match the emission wavelength of the emitter, boosting the radiative decay rate by more than one order of magnitude and maintaining a high quantum yield. As a result, all-round enhancements in the fluorescence emission are achieved. Preliminary studies show that the hybrid stack nanoantenna can produce two times more fluorescence enhancement, and 20 times larger far field intensity comparing to those of a pure metallic nanoantenna. On top of that, around 70% of the overall radiation has been directed towards the dielectric cap side, which would be beneficial to the collection efficiency. This design fully leverages the advantages of both metal and dielectric, which could be useful in the fluorescence enhancement applications.

Under extreme conditions, when the coupling between photon and exciton is sufficiently strong, a hybridised quantum state called polariton is formed. Polaritons exhibit intriguing features, such as Bose-Einstein condensation and Rabi splitting, and have applications in many areas, including molecular sensors, light harvesting and quantum optical devices. Previously polaritons are often produced in microcavities at low temperatures, with a cavity volume at the order of m3. Plasmonic junctions provide extreme confinement and enhancement of optical fields within ~nm3 cavity, about 8-9 orders smaller than that of microcavity, thus producing extremely strong Purcell effect, which renders the observation of strong-coupling between plasmon and exciton at room temperature, so called plexciton. Here we report the observation of strong coupling between localised surface plasmon (LSP) and the excitons of fluorescent graphene quantum dots. We adopt a nanoparticle-on-mirror (NPoM) plasmonic structure, comprised of a Au nanoparticle on top of a reflective Au substrate (the 'mirror'). Extremely strong field enhancement is produced within the nanometer-scale junction. The Au nanoparticle is encapsulated with a thin layer of graphene shell. The measured scattering spectra of Au nanoparticles show distinct splitting double peaks, a characteristic feature of strong coupling. In addition, we demonstrate that the strong coupling is configurable. The splitting can be tuned with a low-power laser irradiation, exhibiting typical anti-crossing behaviour as a result of tuned LSP resonance and the oscillator strength of nano graphene. Our results demonstrate a new avenue for investigating strong-coupling at room temperature and provide opportunities for developing tuneable quantum optical devices.

Conventional optical components are limited to size-scales much larger than the wavelength of light, as changes to the amplitude, phase and polarization of the electromagnetic fields are accrued gradually along an optical path. However, advances in nanophotonics have produced ultrathin, so-called “flat” optical components that beget abrupt changes in these properties over distances significantly shorter than the free space wavelength. While high optical losses still plague many approaches, phonon polariton materials have demonstrated long lifetimes for localized modes in comparison to plasmon-polariton based nanophotonics. Our work predicts a further 14-fold increase in the optic phonon lifetime and we experimentally report a ~3-fold improvement through isotopic enrichment of hexagonal boron nitride (hBN). We establish commensurate increases in the phonon polariton propagation length via direct imaging of polaritonic standing waves by means of infrared nano-optics. Our results provide the foundation for a materials-growth-directed approach towards realizing the loss control necessary for the development of phonon polariton based nanophotonic devices.

Uncooled microbolometric photodetection is a key technology for low cost, reliable and lightweight infrared sensing but suffers in performance compared to cooled photodetectors. Introducing new microbolometer functionality such as wavelength and polarisation sensitivity will improve current device performance and encourage new market opportunities. One method is to introduce metallic nanostructures, which are widely known to exhibit strong localised surface plasmon resonances (LSPR) that are sensitive to incident wavelength and polarisation. This work presents the integration of plasmonic silver nanorods into the material vanadium dioxide VO₂. An experimental correlation between suppression of VO₂ resistivity and dips in transmission spectra was observed. Subsequent optical and thermal simulations of VO₂ films, both on sapphire Al₂O₃ and suspended in air, demonstrate how LSPR-driven electric field enhancement leads to localised heating around the nanorods and subsequent temperature distribution on the nanoscale. This work opens the path to a broad family of photodetection functionalities for vanadium dioxide-based microbolometers.

Optical polarization is an important characteristic of electromagnetic waves that has a significant impact on number of applications, such as information delivery, 3D imaging, and quantum computation. Metasurfaces, sort of artificially designed planar structure, have attracted immense attention due to their ability to control the amplitude and phase of electromagnetic waves at a subwavelength scale. Metasurfaces hold promise for the fields of nonlinear dynamics, light beam shaping, quantum computation, etc. Beside these promising applications, metasurfaces can also be used for versatile polarization generation in a compact device dimension. Therefore, metasurfaces can be used for creation of flat optical devices with novel functionalities. In this talk, I will discuss how we can generate versatile polarization states by using metasurfaces. Firstly, I will describe geometric phase metasurfaces, which can be used for passive polarization control. We demonstrate six metasurface chips integrated on a single sample, in which each chip is responsible for generating one specific polarization state thus generating versatile polarization sates. Subsequently, I will discuss a scheme of active polarization modulation by using indium tin oxide (ITO)-based tunable metasurfaces. By suitably biasing the metasurface, the linearly-polarized incident light can be actively converted to a cross-polarized, circularly-polarized or elliptically-polarized light.

The limits of electronic, optical and thermal performance of these materials are determined by their atomic-scale dynamics. In order to surpass conventional, bulk properties of materials, an accurate description of excited-state phenomena is essential. Light-matter interactions and electronic excited-state phenomena require high-level electronic structure methods beyond the all-pervasive density-functional theory. Simultaneously, the properties of interest are fundamentally non-equilibrium and require techniques that are reliable beyond small perturbations from equilibrium. Electron-photon, electron-electron as well as electron-phonon dynamics and far-from-equilibrium transport are critical to describe ultrafast and excited-state optoelectronic interactions in materials. Ab initio descriptions of phonons are essential to capture both excitation and loss (decoherence) mechanisms, and are challenging to incorporate directly in calculations due to a large mismatch in energy scales between electrons and phonons. In this talk I will show the first results using a new theory method we have developed to calculate arbitrary electron-phonon and electron-optical interactions in a Feynman diagram many-body framework integrated with a nonequilibrium carrier transport method (NESSE). Further, I will discuss a new formalism at the intersection of cavity quantum-electrodynamics and electronic structure methods, quantum-electrodynamical density functional theory (QEDFT), to treat electrons and photons on the same quantized footing. Finally, I will demonstrate how phonons are formally included in QEDFT to predict new single molecule - cavity optomechanical effects.

We study theoretically and numerically high density of states for hyperbolic bilayered metamaterials (HMM). It reveals that density response of HMMis reminiscent of Fermi electronic band structure of metal or semiconductors. By the method of Green function a van Hove type singularity is found in photonic density spectra of HMM with saddle point localization on photonic Fermi surface (FS) of metamaterial Similar to the electronic systems, the photonic FS close to Van Hove singularity experiences instabilities induced by the changes in volume fractions of its constituents that leads to the Lifshitz type zero-temperature phase transition between FS of types I and II hyperbolic states at the protected by topology critical point.

We present progress on the experimental observation of exceptional points (EPs) in passive plasmonic nanostructures. The system has EPs which are degeneracies in open wave systems where at least two energy levels and their corresponding eigenstates coalesce. They manifest themselves by the simultaneous degeneracy of both resonant frequencies and its linewidths. We consider a plasmonic system based on a multilayer plasmonic structure with structural offset [1, 2]. The realization of an EP via hybridized modes requires the control of at least two physical parameters. The two parameters used for the above system to reach an EP are the shift between bars and the periodicity.

We exploit the transverse optical spin of the eigenmodes of plasmonic silver nanowires to direct the emission of specific valleys in a 2D material. The large confinement of the plasmonic modes leads to a large transverse optical spin. As a result, we are able to couple valleyinformation with 90% efficiency to plasmonic propagation direction. (Science, Jan. 26, 2018)

Optical metasurface can provide control over wavefront, polarization and spectrum of light fields while having just nanoscale thickness, making them promising candidates for flat optical components. Most metasurfaces studied so far consist of two-dimensional subwavelength arrays of designed metallic or dielectric scatterers. Deviations from a periodic, ordered arrangement are usually associated with a deterioration of the optical properties. However, the introduction of controlled disorder also provides interesting opportunities to engineer the optical response of metasurfaces. For example, the introduction of disorder can decrease unwanted anisotropy in the optical response [1], it suppresses scattering into discrete diffraction orders, and it can enhance the metasurfaces’ channel capacity [2]. Here we investigate different types of disordered metasurfaces. We demonstrate that the introduction of rotational disorder at the unit-cell level enables the realization of chiral plasmonic metasurfaces supporting pure circular dichroism and circular birefringence. We show experimentally that the polarization eigenstates of these metasurfaces, which coincide with the fundamental right- and left-handed circular polarizations, do not depend on the wavelength over the spectral range of the metasurface resonances. Thereby, our metasurfaces mimic the behaviour of natural chiral media, while providing a stronger chiral response. Furthermore, we systematically investigate how the introduction of different types of positional disorder influences the complex transmittance spectra of Mie-resonant silicon metasurfaces, showing that disorder provides an independent degree of freedom for engineering their spatial and spectral dispersion. [1] S. S. Kruk et al., Phys. Rev. B 88, 201404(R) (2013). [2] D. Veksler et al., ACS Photonics 2, 661 (2015).

We investigated a mechanism for quick release and transfer of gold nanoparticles (GNPs) from a soft substrate to another substrate under laser illumination. The heating of GNPs on a soft substrate with a continuous-wave laser causes a rapid thermal expansion of the substrate, which can be used to selectively release and place GNPs onto another surface. In-plane and out-of-plane nanostructures are successfully fabricated using this method. This rapid release-and-place process can be used for additive nonmanufacturing of metallic nanostructures under ambient conditions, which paves a way for affordable nanomanufacturing and enables a wide variety of applications in nanophotonics, ultrasensitive sensing, and nonlinear plasmonics.

We have developed a far-field optical approach capable of mapping the local density of states (LDOS) of plasmonic structures with a spatial resolution in the order of ~10nm, well below the diffraction limit of light. Our method is based on the simultaneous localization of single fluorescent emitters with an EM-CCD camera, and the detection of their fluorescence lifetime with a time-resolved avalanche photodiode. This approach is compatible with unknown and non-periodic samples, as it makes use of a dense labeling strategy with photoactivatable fluorophores who are stochastically activated over time. We demonstrate the performance of our technique by studying the lifetime reduction induced by a silver nanowire, obtaining a super-resolved mapping of the LDOS with a localization precision of 6 nm and a temporal resolution down to 100 ps. We believe that our technique, which can be implemented in any wide-field inverted microscope, does not require scanning parts, and performs far-field measurements at the molecular level, opens up a wide range of applications spanning from nanophotonics to biological imaging.

Plasmon-enhanced absorption, often considered as a promising solution for efficient light trapping in thin film silicon solar cells, suffers from pronounced optical losses i.e. parasitic absorption, which do not contribute to the obtainable photocurrent. Direct measurements of such losses are therefore essential to optimize the design of plasmonic nanostructures and supporting layers. Importantly, contributions of useful and parasitic absorption cannot be measured separately with commonly used optical spectrophotometry. In this study we apply a novel strategy consisting in a combination of photocurrent and photothermal spectroscopic techniques to experimentally quantify the trade-off between useful and parasitic absorption of light in thin hydrogenated microcrystalline silicon (μc-Si:H) films incorporating self-assembled silver nanoparticle arrays located at their rear side. The highly sensitive photothermal technique accounts for all absorption processes that result in a generation of heat i.e. total absorption while the photocurrent spectroscopy accounts only for the photons absorbed in the μc-Si:H layer which generate photocarriers i.e. useful absorption [1]. We demonstrate that for 0.9 μm thick μc-Si:H film the optical losses resulting from the plasmonic light trapping are insignificant below 730 nm, above which they increase rapidly with increasing illumination wavelength. For the films deposited on nanoparticle arrays coupled with a flat silver mirror (plasmonic back reflector), we achieved a significant broadband enhancement of the useful absorption resulting from both surface texturing and plasmonic scattering, and achieving 91% of the theoretical Lambertian limit of absorption. [1] S. Morawiec et al. Experimental Quantification of Useful and Parasitic Absorption of Light in Plasmon-Enhanced Thin Silicon Films for Solar Cells Application. Scientific Reports 6 (2016)

We report on a new class of plasmonic nanogratings in which the gradient in the groove-width enables facile fabrication of multiwavelength surface-enhanced Raman spectroscopy (SERS) substrates. These substrates have the potential of achieving unprecedented detection sensitivity, specificity and speed. The structure of these nano-gratings consist of metal-insulator-metal grooves with a 40 nm central groove width flanked by a series of grooves on either side with gradually increasing width. Groove widths increase in steps of 5 nm up to a maximum width of 200 nm positioned farthest from the central groove on either side. The gradient in groove width in turn produces a gradient in the effective refractive index of the grating determined by the groove width at each location. Together, multiple laser wavelengths can be simultaneously confined to the centrally situated narrow grooves, with the neighbouring larger grooves guiding the nonlocalized waves toward the grating center from both directions. This generates a maximally enhanced plasmonic field over a broad range of wavelengths on the surface of the nanograting which can be used to increase the Raman scattering efficiency of a sample molecule distributed over the structure. The structures were fabricated using electron beam lithography, reactive ion etching, and sputter-deposition techniques. Experimental results demonstrated up to four orders of magnitude enhancement in the SERS intensity of 1 mM phospholipid samples deposited over the graded nano-gratings. In addition, characterization of the phospholipids in aqueous phase flowing over the nano-gratings integrated within a microfluidic device revealed that the Raman peaks were only detectable with the enhancement introduced by the grating. These results were obtained using 532, 638, and 785 nm lasers, demonstrating the multispectral sensing capability of the graded gratings for static and dynamic characterization of low concentration species.

Plasmonic oligomers allow new ways to manipulate nonlinear optical effects such as second-harmonic generation (SHG) through collective resonances. However, earlier techniques to probe such effects have relied mostly on the use of plane waves or focused beam excitations with homogenous states-of-polarization (e.g., linear) that obviously do not match the spatial symmetries of the oligomer. Here, we investigate collective effects in the SHG from individual plasmonic oligomers using microscopy with cylindrical vector beams such as radial or azimuthal polarizations. The oligomers were prepared by electron-beam lithography. The oligomers consisted of gold nanorods that have a longitudinal plasmon resonance close to the fundamental wavelength that is used for SHG excitation and whose long axes are arranged locally such that they follow the distribution of the transverse component of the electric field of radial or azimuthal polarizations. We found that SHG from such oligomers is strongly modified by the interplay between the properties of the incident cylindrical vector beam and interparticle coupling. We find that the oligomers with radially-oriented nanorods exhibit small coupling effects. In contrast, we observed that the oligomers with azimuthally-oriented nanorods exhibit large coupling effects that lead to silencing of SHG from the whole structure. We found good qualitative agreement between our experimental findings and calculations using the method of moments. The work describes a new route to investigate coupling effects in arrangements of nanostructures and thereby to control the efficiency of nonlinear effects in these structures.

The optical nonlinear effects can provide different advanced electromagnetic functionalities, such as wave mixing and phase conjugation, which can be applied in a variety of new applications. However, these effects usually suffer from extremely weak nature and require high input intensity values in order to be excited. Interestingly, the large third order nonlinearity of graphene, along with the strong field confinement stemming from its plasmonic behavior, can be utilized to enhance several relative weak nonlinear effects at infrared (IR) and terahertz (THz) frequencies. Towards this goal, various nonlinear graphene metasurfaces are presented in this work to effectively increase the efficiency of different optical nonlinear effects and, as a result, decrease the required input intensity needed to be excited. In particular, we will show that the efficiency of four-wave mixing (FWM) can be improved by several orders of magnitude by using a nonlinear metasurface composed of patterned graphene ribbons, a dielectric interlayer, and a metallic reflector acting as substrate. We also demonstrate that the self-phase modulation (SPM) nonlinear process can be enhanced by using an alternative graphene nonlinear metasurface, operating as coherent perfect absorber, leading to a pronounced shift in the resonant frequency of the coherent perfect absorption (CPA) effect of this structure as the input intensity of the impinging incident waves is increased. This property will provide a robust mechanism to dynamically tune and switch the CPA process. Furthermore, it will be presented that strong negative reflection and refraction can be achieved by a single graphene monolayer film due to the enhancement of another nonlinear process, known as phase conjugation. This nonlinear process is envisioned to be used in the construction of a perfect imaging device with subwavelength resolution.

Stimulated Brillouin scattering (SBS) is a strong nonlinear interaction between optical and mechanical modes of nanophotonic waveguides, whereby the optical field can generate and maintain extremely strong acoustic waves. Until recently, it was believed that the high losses associated with metals would render SBS unmeasureable in plasmonic systems. However recent work has shown that the confinement of acoustic modes in metallic structures, together with strong field gradients that occur on metal-dielectric surfaces, can result in SBS gain orders-of-magnitude greater than that in dielectric waveguides. This gain scales such that it is able to overcome the intrinsic loss of some surface plasmon polariton (SPP) configurations, depending on the waveguide geometry. Here we examine the interaction of light and sound in plasmonic systems, including the forces and scattering processes in the presence of highly-lossy optical and acoustic modes. We examine the thermal effects arising from the optical loss and show how the measured gain is determined by the CW power-handling capabilities of the plasmonic mode. We examine a range of possible waveguide geometries and establish relevant Figures of Merit for evaluating a range of realistic plasmonic waveguides, and examine how geometrical scaling affects the SBS gain in both forward (co-propagating) and backward (counter-propagating) SBS configurations. We find that SPP-driven SBS will be measureable within a broad range of waveguides, and present general design rules for measuring SBS in different material systems. Finally, we discuss the challenges and opportunities for harnessing this effect in the first experiments.

Due to its symmetry properties, second-harmonic generation in plasmonic nanostructures enables the observation of even-parity modes that couple weakly to the far field. Consequentially, those modes radiate less and thus have a longer lifetime. Using a full-wave numerical method, we study the linear and second harmonic dynamical responses of a silver nanorod under plane-wave femtosecond pulse illumination. Depending on the spectral position and duration of the pulse, the decaying field of the different modes can be separated, and the free oscillations of each mode are well fitted by a damped harmonic oscillator model, both in the linear and nonlinear regimes. Additionally, interference effects between different modes excited at the second harmonic are observed.

High-refractive-index (HRI) dielectric metasurfaces have attracted a lot of attention recently due to their advantages of low non-radiative losses and high melting temperatures. Silicon is one of feasible HRI materials that has been widely used in solar cells, photonic waveguides, and photon detectors. However, the band-gap ~ 1 eV makes the quantum efficiency of silicon low at near-infrared (NIR) wavelengths. In this work, a high absorptance device is proposed and realized by using amorphous silicon nanoantenna arrays (a-Si NA arrays) that suppress backward and forward scattering with engineered lattice resonance with Kerker effect. The overlap of electric dipole and magnetic dipole resonances is experimentally demonstrated. The absorptance of a-Si NA arrays increases 3-fold in the near-infrared (NIR) range in comparison to unpatterned silicon films. Nonradiating a-Si NA arrays can achieve high absorptance with a small resonance bandwidth (Q = 11.89) at wavelength 785 nm.

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.

Both the strong mode confinement and the low propagation loss are longed for designing highly integrated terahertz (THz) devices, but they are difficult to be achieved at the same time. Here, a graphene-coated nanowire with a dropshaped cross section (GNDCS) is proposed with the long-range propagation and strong confinement. We found this waveguide can support two kinds of graphene surface plasmon polaritons (GSPPs), outside-dominant and insidedominant modes, with distinctly different energy distributions. Interestingly, both modes can achieve low-loss propagation with strong mode confinement. In particular, the outside-dominant mode can attain an extremely long propagation length (1mm) and the inside-dominant mode has a very high energy utilization rate. These excellent characteristics make the waveguide very useful in the nanophotonics, bio-photonics and highly integrated THz circuits.

Typical many-wavelength scale of the optical fiber-integrated photonic elements (for example, ring resonators, Bragg reflectors, Mach-Zehnder interferometers, etc.) has been an insuperable obstacle for the realization of truly integrated photonic circuits that would have the dimensions compliant with the semiconductor industry standards. Doped graphene however, promises the deeply subwavelength size of the plasmonic-based optical elements due to the very short plasmon wavelength. In this work, we propose a design of the ultra-compact fiber-integrated optical switch based on the graphene-functionalized plasmonic nano-cavity for ultrafast light modulation. Presence of graphene allows to actively control the plasmonic resonance in the cavity via the electrostatic doping, so that properly tuned Fermi level in graphene results in a strong constructive (destructive) Fano interference between the propagating mode in the fiber and the graphene plasmonic mode in the nano-cavity, increasing (zeroing) the transmission efficiency at given frequency. The nano-cavity effectively works as a plasmonic Fabry-Perot resonator, significantly enhancing the coupling efficiency as well as the interference strength. Due to the strong confinement of graphene plasmons, the active volume of the switch can be as small as 10^–3λ₀ ^–3, making it possible to build an optical circuit with a very high density of elements. Furthermore, sharp profile of the Fano resonance provides a fast switching speed even with small variation of doping. Therefore, proposed design requires very low driving voltage of ~1V, while providing the modulation depth of at least 0.5.

Mechanism of low-energy optical absorptions in tungsten oxide and tungsten bronzes is still a matter of controversy, although plasmon and polaron mechanisms have been proposed as a dominant cause. In this report we studied Cs-doped hexagonal tungsten bronze (Cs-HTB) nanoparticles (NPs), known as a solar-control material, and show systematic analysis results on structural and optical changes with varied amount of oxygen vacancy (V_O) and alkali content. Chemical analysis of the Cs-HTB samples synthesized under a reducing gas flow revealed that their exact composition is described as Cs_xWO_3-y (y ≤ 0.46). With increasing Cs⁺ and V_O, lattice constants determined by XRD Rietveld method changed linearly and optical absorption peaks observed at 0.5-2.0 eV were found to intensify. The origin of the structural change is considered to be the destabilization of the pseudo Jahn-Teller distortion in WO₆ octahedra. The optical peaks were analyzed by the Drude-Lorentz analysis assuming coexisting anisotropic plasmon resonances and a polaron excitation, and by the Mie integration method to incorporate the ensemble inhomogeneity effect of NPs. This procedure enabled complete deconvolutions of the optical peaks, which indicated that the polaron absorption was caused by the localized electrons derived from V_O.

A new optical sensor based on the surface plasmon resonance (SPR) is proposed and characterized. The sensor is composed by sandwiching the graphene sheets between two metal films in the Kretschmann configuration. The resonance angle and the sensitivity of proposed sensor are analyzed through the transfer matrix method. Moreover, the refractive index change of the analyte can be detected accurately by using the proposed sensor. It is observed that the sensitivity of the proposed bimetallic sensor configuration can be greatly enhanced than conventional single metal configuration by optimizing the thickness of the metals and the number of graphene layers. Finally, we believe that the proposed SPR configuration can further promote the biosensing application.

Plasmonic-induced transparency (PIT) in the metal-insulator-metal plasmonic waveguide with two side-coupled rectangular ring disk structures is numerically investigated. The PIT resonance occurs as a consequence of the destructive interference between the two structures. It is found that the transmittance can be easily adjusted by changing the parameters of the structure and coupling distance between the structure and waveguide. By optimizing the parameters, the transmittance of the structure can up to 75% in our discussion. These results may have important applications for designing integrated devices such as narrow-frequency optical filters, novel sensors and high-speed switches.

In this work, we demonstrated a new method for coupling light, using prism with a small index of refraction and surface plasmon polaritons (SPP), into a crystalline silicon (Si) waveguides and performed simulation work using Lumerical FDTD Solutions. The designed structure is comprised of a dielectric prism, air-gap, metal (Ag) film, Si and silicon dioxide (SiO₂). The system follows the Otto configuration for the excitation of SPP which includes a fused silica prism and a 100 nm layer of silver metal sputtered on top of SiO₂ with an air-gap between the prism and the metal film. A 0.75×100 μm (height×width) silicon waveguide with tapered coupler is located on the same buried oxide along the silver layer for optical input channel. A p-polarized (TM mode) light with an incident angle of 44° at the wavelength of 1550 nm is incident at the interface of the fused silica/air-gap to excite the SPP. The 2D simulation shows a coupling efficiency of 54% which reveals the potential for application of this I/O coupling method in silicon photonics. For proof of concept, we fabricated and characterized the materials layout described above on an SOI substrate. For the Si structure, a tapered coupler and waveguide is fabricated using a XeF₂ dry-etch and lift-off for the metal structure. Also, the experimental setup is suggested to locate the prism on the right position of the wafer and measure the output light from the waveguide by butt coupling.

Infrared spectroscopy is very powerful tool to analyze the chemicals based on their molecular signatures. The registration of the fundamental vibrational modes that lie in the far IR is extensively explored, however the excitation of derivatives namely high harmonics molecular vibrations overtones is still a mystery. Although the absorption crosssection of molecular transition overtones is order of magnitude smaller compared to their fundamental vibrations, the research of overtones is of high importance if just would be possible to detect them. In this work, we show that the challenge in detection of molecular overtones may be overcome with localized surface plasmon resonance effect in gold nanorods antennas. We use N-Methylaniline as a probe molecule since we confirmed the excitation its molecular transitions overtones in near-infrared around 1.5 μm. We calculate absorption cross-section of gold nanorods with fixed diameter of 10 nm and different lengths varying from 80 to 160 nm surrounded by a homogeneous medium with the optical properties of N-Methylaniline, using the finite element method (FEM). To single out the contribution of the overtone modes, computations were repeated with N-Methylaniline replaced by the dispersionless media mimicking only the mean value of N-Methylaniline refractive index, n = 1.5712, and eliminating absorption. We show, that the differential absorption in the spectral range of the first overtone of the -NH vibration located at 1492 nm and the first overtone of the -CH vibration located at 1676 nm have both positive and negative values due to the shifting of the gold nanorod plasmon resonance band.

We present a novel design for an axisymmetric, three-dimensional tapered dome shaped nanoantenna structure similar to nanocones. The proposed design is modelled and analyzed using numerical simulation employing the finite element method (FEM) on COMSOL. Tapered structures have emerged as promising devices in efficiently guiding and localizing free-space radiation near the apex when excited by an external electric field, thus promoting a stronger light–matter interaction. Such metallic vertically tapered structures similar to nanocones provide strong filed enhancement at the tip when the resonance condition is fulfilled and hence most design applications of such structures rely on excitation produced at the tip. In this study the traditional nanocone structure is modified to form a tapered minaret structure comprised of multiple layers and an onion-shaped crown. Enhancement factors of the order of 10⁴ are obtained at the tip at resonance with high directivity, thus providing an accessible hot spot. These features make the structure particularly suitable for use as nanoprobes for tip-enhanced Raman spectroscopy (TERS), scanning nearfield optical microscopy (SNOM), and surface plasmon polaritons enhanced Raman scattering (SPPERS).

In this paper, a pair of hollow bow-tie nanoantenna with a feed gap has been designed using gold in the visible frequency range. This nanoantenna exhibits a strong field enhancement in the feed gap region at the resonance wavelength due to the localized surface plasmon. The absorption cross-section of this nanoantenna has been compared with the solid bowtie nanoantenna and it has been observed that the absorption cross section in hollow bowtie nanoantenna is less as compared to solid bowtie nanoantenna. This is because of the less volume availability for light absorption in the hollow bowtie nanoantenna. So, the main reason of using a hollow bowtie over a solid bowtie is the reduced absorption cross-section. Further, properties of hollow bowtie nanoantenna have been enhanced by geometric optimization using COMSOL Multiphysics software.

Noble metal nanoparticles are strong absorbers of incident radiation in a tailorable fashion. Several solutionprocessed methods of fabricating metallic nanostructures exist. For large area solar cells, it is essential that the developed ink be cost-effective and reasonably overlap with the solar spectrum. In this work, we report the development of light-mediated synthetic method under various light sources, involving the evolution of spherical silver nanoparticles into large anisotropic silver nanoparticles of variable sizes. Reduction of silver nitrate in an aqueous sodium citrate solution results in spherical Ag nanoparticles that turned the stock solution yellow. The solution was aged under various light sources. Broadband (400-1400 nm) absorption was observed for the resulting ink. This synthesis method is thus potentially suitable for an industrial scale process for inks with a tailorable match with the solar spectrum (AM1.5G).

In this manuscript, a technique to realize multifunctional anisotropic nanoparticles with small size distribution in large quantities is presented. The fabrication of the nanoparticles is based on Ultraviolet Nanoimprint Lithography (UV-NIL), physical vapor deposition and lift-off processes in order to finally disperse the nanoparticles in solution. The particles are designed for in-vitro biomolecular diagnostics. The underlying homogeneous biomolecular sensing method is based on the optical detection of changes in the rotational dynamics of anisotropic hybrid nanoparticles immersed in the sample solution, such as blood. [1], [2] This approach requires highly monodisperse nanoparticles in order to achieve a high sensitivity in molecule detection. The fabrication method based on UV-NIL and lift-off processes holds several advantages compared to chemical synthesized nanoparticles, like very small size variations and engineering freedom in particle geometry. We demonstrate the fabrication of elliptical particles with an area size of 1,557 × 10^(-12)m² ±3%.

Localized surface plasmons have been reported for periodic 2D monolayer black phosphorene (BP) nanoribbons in the infrared region. The anisotropic nature of BP causes different plasmonic effects depending on their orientation over select dielectric substrates, leading to tunability and promising future applications in imaging and other detectors. Computational models are used to demonstrate that by tuning the localized plasmonic resonance, as well as the orientation of the BP nanoribbon, it is possible to obtain desired coupled resonance modes and enhanced absorption capabilities. The modes obtained from the absorption spectra span the infrared range and extend our understanding of BP plasmons.

Photonic integrated circuits (PICs) have been a very active research area ever since the inception of integrated optics for the application of the wavelength division multiplexing networks. One of the main size limitations to regular integrated optics based circuits is the weak optical confinement. This makes it very difficult to change the direction of optical waveguides in a very short distance with low loss. Photonic band gap based approaches offer promise of compact waveguide size that can be bent over very rapidly. However, wavelength dependence and the fabrication difficulty remain to be the challenges. On the other hand, advances in nanofabrication and full-wave electromagnetic simulation techniques have permitted the design and realization of a wide variety of plasmonic waveguide structures as excellent candidates for future nanoscale electronic-photonic integrated circuits. In this paper, we reported the nano-gap resonator with the straight waveguide without the ring shape resonator, which is replaced with a straight waveguide, metalic layer, and nano-gap. We investigated the resonant properties of the structure using the FDTD method. The results reveal that the proposed structure has the band stop and lasing characteristic.

PbSe is a well-known IV-VI photoconductive material, typically operating in the 3-5μm regime at temperatures easily achieved with compact thermoelectric coolers. Recently, Northrop Grumman Corporation has demonstrated PbSe photoconductive pixels down to 12x12 μm2, with quantum efficiencies as high as 15% at 230K. Today’s challenges, however, demand more sensitivity at near room-temperature operation. To this end, the employment of nanoplasmonic antenna for the increased performance of PbSe-based photoconductors has been investigated. Metallic nanostructures have seen a great deal of interest in recent years, due to increased absorption and large field enhancements at the surface plasmon resonance (SPR). These structures are usually reserved for lower wavelength regimes where the incident radiation matches the plasma frequency of the metal. However, by manipulating the size, morphology and surrounding medium of the structure, the surface plasmon resonance can be shifted to longer wavelengths. Indeed, by tuning the electric permittivity of the host material, size, aspect ratio, or combination thereof, the nanoantenna SPR can be tailored to the infrared band of interest. For PbSe photoconductors tuning these nanostructure parameters can result in a large increase in absorption and sensitivity. Herein, we present an examination of several types of nanoantenna including nanospheres, nanorods, and nanodiscs made from Au, Ag, and Pt in various layers of PbSe photoconductive films. Structures have been modeled using Mie theory to determine SPR, as well as finite element modeling to determine the increase in near-field intensity using the full solution of Maxwell’s equations. The presented results demonstrate large increases in absorption, as well as the near-field enhancement of nanoplasmonic antenna employed in PbSe photoconductive films.

Plasmonic nanoprisms with and without truncation in the form of Au-dielectric- Au and Ag-dielectric- Ag sandwich structures have been simulated using finite-difference time-domain (FDTD) simulation technique. Effect of dielectric material thickness on dipole resonance were studied in detail. Truncation introduced a blue shift in dipole resonance for silver and gold sandwich. For ideal gold and silver sandwich, the dipole resonance was not significantly affected for smaller thickness of dielectric material. However, for truncated sandwiches of gold and silver exhibited a gradual red shift with increase in thickness of dielectric layer. To conclude, the thickness of dielectric layer employed in sandwich can be used as a tunable parameter towards exhibition of dipole resonance regardless of gold or silver.

We proposed a broadband absorber based in rectangular metallic and dielectric grating. The geometric parameters of the proposed structure were optimized to exhibits strong absorption (above 90% for incidence normal) with polarization-independent in the visible spectrum (400-700nm). The proposed structure has demonstrated wide-angle absorption of above 80% for angles of incidence of up to 60° for TM mode and up to 40° for TE mode. The high absorption does not change when we vary other geometric parameters of the structure to analyze the fabrication tolerance.

Asymmetrical absorption plays an important role in applications such as photovoltaics, detectors, modulators and emitters. In this work, we introduce and numerically analyze a broadband device capable of realizing asymmetrical optical absorption depending on the direction of propagation of light. The proposed asymmetrical absorber is designed and optimized by a parametric search based on genetic algorithm.

We present transmission spectra of Au/PTFE nanoparticles in 450 nm to 750 nm wavelength range. Au/PTFE absorption spectra in the above-mentioned spectral range was simulated using Maxwell-Garnett theory of effective dielectric function. We demonstrate that the Maxwell-Garnett theory of effective dielectric function correctly predicts the position of the plasmon absorption band maximum for gold nanoparticles in PTFE matrix.