This PDF file contains the front matter associated with SPIE Proceedings Volume 10346, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

With similar optical properties to gold and high thermal stability, titanium nitride continues to prove itself as a promising plasmonic material for high-temperature applications in the visible and near-infrared. In this work, we use transient pump probe differential reflection measurements to compare the electron energy decay channels in titanium nitride and gold thin films. Using an extended two temperature model to incorporate the photoexcited electrons, it is possible to separate the electron-electron and electron-phonon scattering contributions immediately following the arrival of the pump pulse. This model allows for incredibly accurate determination of the internal electronic properties using only optical measurements. As the electronic properties are key in hot electron applications, we show that titanium nitide has substantially longer electron thermalization and electron-phonon scattering times. With this, we were also able to resolve electron thermal conduction in the film using purely optical measurements.

Plasmonic nanomaterials are known to concentrate incident light to their surfaces by collective electron oscillation. Plasmonic hot-spot refers to locations where electromagnetic fields are particularly enhanced relative to the incident field. Traditional plasmonic nanomaterials are 1D (e.g., colloidal nanoparticles) or 2D (lithographically patterned nanostructure arrays) in nature, which typically result in sparse field concentration patterns. To improve efficiency and better utilization of hot-spots, we investigate 3D plasmonic nanoarchitecture where abundant hot-spots are formed in a 3D volumetric fashion, a feature drastically departing from traditional nanostructures.

Cathodoluminescence makes use of the beam raster capabilities of a scanning electron microscope to excite electrons in a sample and collects the luminescent light to produce images or obtain spectra that can reveal useful information about the sample. This technique has been shown to be particularly interesting for studying the plasmonic oscillations of metallic nanostructures. A recently developed fabrication technique has allowed for the creation of sub-10 nm gaps between metallic nanostructures for use as plasmonically active samples that can be tailored for various potential applications. The high degree of control over the geometries capable of being fabricated via this nanomasking technique allow for unique types of structures that are otherwise difficult to fabricate. In this work, the plasmonic response of metallic structures separated by sub-10 nm gaps is studied via CL imaging. Hyperspectral images can demonstrate the effectiveness with which various geometries produce specific wavelength resonances. The results can be helpful in determining which structures are optimal for specific applications based on these resonances. Also, the images can help to guide future fabrication, as the plasmon modes become better understood.

Microcolumns are widely used for parallel electron-beam lithography because of their compactness and the ability to achieve high spatial resolution. A design of a large array of electrostatic microcolumns for our recent surface plasmon enhanced photoemission sources is optimized numerically. Because of the compactness, one million of microcolumns can be put within 1 cm² area. To avoid the trade-off between resolution and throughput, each microcolumn has one beamlet and there is no crossing point between any of the beamlets. An aperture self-aligned fabrication process is developed to make the optimized microcolumns.

Plasmonic nanoantennas are of interest because of their capability to enhance light-matter interactions. We present new results where antennas are used to obtain nanoscale devices with tunable characteristics. Applications of these devices include electrically controlled antennas, antennas integrated on silicon waveguides, and optical solar reflectors for spacecraft. By using tunable materials such as vanadium dioxide and doped-metal oxides, we demonstrate precise control and active tunability of the optical response. Experimental results are supported by combined electro-optical modelling at the nanoscale.

Surface plasmon polariton (SPP) provide the field enhancement and localization beyond the diffraction limit of light. By using SPP, we have numerically designed tiny resonance sensors as plasmonic integrated devices with silver or gold as metal material for near infrared region of light. We will present our recent work for the sensors. The sensors are the combination of the plasmon resonator and MIM channel plasmon waveguide with the gap of ~150 nm and the hight of ~1.5 micron. The typical area size of sensor is order of 1 square micrometers and their sensitivity for temperature or stress change is comparable to current optical sensors. We have fabricated some fundamental structure of the device by using the electron beam lithography and will show experimental optical characteristics for IR region.

Optical properties of two-dimensional periodic systems of the dielectric micro bars and micro cones are investigated. Computer simulations as well as real experiment reveal anomalous optical response of the dielectric metasurface due to excitation of the dielectric and metal-dielectric resonances, which are excited in-between metal nanoparticles and dielectric cones and bars. In the metal-dielectric resonance local electric field can be orders on magnitude larger than the field in the plasmon resonance only. To investigate local electric field the signal molecules were deposited on the metal nanoparticles. We demonstrate the enhancement of the electro- magnetic field by detecting the Raman signal from the of organic acid molecules deposited on the investigated metasurface.

Plasmonic nano structures fabricated using inexpensive and abundant aluminum metal shows intense narrow reflection peaks with strong response to the external stimuli, provides a simple yet powerful detection mechanism that is well suited for the development of low cost and low power sensors, such as colorimetric sensors, which transduces external stimuli or environmental changes in to visible colour changes. Such low cost and disposable sensors have huge demands in the point-of-care and home health care diagnostic applications. We present the design of a colorimetric sensing platform based on reflection mode plasmonic colour filters on both silicon and glass substrate, which demonstrate a sharp colour change for varying ambient refractive index. The sensor is essentially a plasmonic metamaterial in which the aluminum square plate hovering on a PMMA nano pillar in the background of a perforated aluminum reflector forms the unit cell which is arranged periodically in a 2D square lattice. The meta-surface has two distinct absorption peaks in the visible region leaving a strong reflection band, which strongly responds to the ambient refractive index change, provides a means for the realization of low cost colorimetric sensing platform.

Nanoporous gold is a very promising material platform for several plasmonic applications. Nanoporous gold can be formed by dealloying Au–Ag alloys, previously grown by means of Ag-Au co-sputtering. The optical response is completely determined by the nanostructured film features, that only depend on the initial alloy composition. It has been extensively used as SERS substrate both as thin film and nanofabricated fancy designs. Here we explore the potential application of nanoporous gold as SERS substrate as it is coupled and decorated with Ag nanoparticles. Significant enhancement has been observed in comparison with bare nanoporous film.

We use a near-field microscope to visualize the nanoscale light patterns, both electric and magnetic fields [1,2]. The interplay between the various components of either the magnetic or the electric fields leads to optical entities that, in their size, put nanophotonics to shame: these optical singularities have a size zero. Interestingly, optical singularities near nanoscale structures exhibit a markedly different behavior from those in macroscopic beams [3,4]. We observe a distinctly different behavior around plasmonic nanowires to that above photonic crystal waveguides [5]. Moreover, we show that these singularities and their associated local helicity can be applied for new quantum technology as they can be used to deterministically couple a spin-transition to emission direction [6], useful for novel quantum technology [7]. In addition we show that plasmonic nanowires are better than dielectric waveguides for the transmission of ultrashort pulses [8]. This can also be used to induce nonlinear phenomena [9]. [1] B. le Feber, et al., Nature Photonics Vol. 8, 43-46, (2014). [2] N. Rotenberg and L. Kuipers, Nature Photonics Vol. 8, 919-926, (2014). [3] N. Rotenberg, et al., Optica 2, 540-546 (2015). [4] L. De Angelis, et al., Phys. Rev. Lett. 117, 093901 (2016). [5] I.V. Kabakova, et al., Scientific Reports 6, 22665-1/9 (2016) [6] B. le Feber, et al., Nature Communications 6, 6695 (2015). [7] A. B. Young, et al., Phys. Rev. Lett. 115, 153901 (2015). [8] M. Wulf, et al., ACS Photonics 1, 1173−1180 (2014). [9] A. de Hoogh, et al., ACS Photonics 3, 1446-1452 (2016).

Thorough analysis of the plasmonic phenomena requires proper account for such effects as size dependent plasmon resonance shifts and intensity changes observed in metal nanoparticles, especially in systems with small feature sizes. Recent theoretical advances, including Generalized Nonlocal Optical Response (GNOR), allow to accurately resolve these effects within the classical electromagnetics, paving the way for implementation of efficient low cost computational techniques. We present a new GNOR-based numerical scheme of the flexible Discrete Sources Method for analysis of light scattering by single plasmonic nanoparticle in the layered medium with rigorous account for both substrate-particle interaction and nonlocal effects.

Based on the concept of drawing equivalence between different configurations in transformation optics, we introduce a conceptual framework to investigate radiation from accelerating particles using chains of metamaterial atoms with SOI on a metasurface. The framework allows a global geometric picture in visualizing different one-dimensional space-times in general relativity using our two-dimensional metasurface. In particular, chains of metamaterial atoms along different curved lines in generating a common SPP caustic represent the same particle motions observed in difference reference frames, with relative motion through a general-relativistic transformation, such as a Rindler transformation from a reference Minkowski space-time. Such a tool allows us to study particle motions in different space-times in general while the particular geometric understanding provides us unique ways in generating SPP.

We obtain an eigenmode expansion of the electromagnetic Green’s tensor G(r,r') for lossy resonators in open systems, which is simple yet complete. This enables rapid simulations by providing the spatial variation of G₀(r,r') over both r and r' in one simulation. Few eigenmodes are often necessary for nanostructures, facilitating both analytic calculations and unified insight into computationally intensive phenomena such as Purcell enhancement, radiative heat transfer, van der Waals forces, and Förster resonance energy transfer. We bypass all implementation and completeness issues associated with the alternative quasinormal eigenmode methods, by defining modes with permittivity rather than frequency as the eigenvalue. Thus, modes decay rather than diverge at infinity, and are defined by a linear eigenvalue problem, readily implemented using any numerical method. We demonstrate its general implementation in COMSOL Multiphysics, using the default in-built tools.

Optically resonant dielectric nanostructures is a new direction in nanophotonic research which gives a strong promise to compliment or substitute plasmonics in many potential application areas [1]. The main advantages of resonant dielectric nanostructures over conventional plasmonics are low losses, wide range of applicable dielectric materials and strong magnetic resonant response. So far most of research in this field has been conducted with silicon as a material for nanostructures due to its one of the highest value of refractive index at optical frequencies and CMOS compatibility. However, while silicon is an excellent material of choice for operation in the near-IR spectral range its applicability for visible frequencies is limited by increasing losses inside the material. Also, being an indirect bandgap semiconductor it is not a suitable material for making active nanoantenna devices. For these reasons in recent studies research focus starts shifting towards other appropriate materials such as III-V semiconductors, e.g. GaAs or GaP, and wide-bandgap semiconductors such as TiO2. In this presentation we will discuss applicability of different dielectric/semiconductor material platforms for obtaining resonant nanoantennas and metasurfaces operating in the visible frequency range. We will first show that titanium dioxide metasurfaces can be designed to obtain sharp resonances and full phase control at all three RGB wavelengths through Huygens’ metasurface approach, which pave the way towards realization of thin multi-layer metasurfaces with multi-colour operation. Then we will introduce a new III-V material platform based on GaN, which is highly transparent through the whole visible spectrum, and show high-efficiency operation of GaN metasurfaces in the blue and green parts of the visible spectrum. Finally we will discuss active nanoantennas based on GaAs and show the path towards achieving laser emission from resonant semiconductor nanoantenna structures. References: 1) A. I. Kuznetsov et al., “Optically resonant dielectric nanostructures”, Science 354, aag2472 (2016).

Planar photonic metasurfaces, exhibiting artificial optical effects at the interface, are enabling a broad variety of possibilities as optical elements, communications, and signal processing. The signal we perceive from a metasurface is determined by the phases of the different nanostructures that compose the system. This phase controls the spatial radiation distribution following Huygens’principle and has been utilized in planar optical devices exhibiting negative refraction, cloaking, and holographic elements to name a few. In this presentation, we will first demonstrate the quantitative direct measurement of the phase front produced by a metasurface using digital holography microscopy. We will then show that by designing and tuning the multipolar components of the nanostructured building blocks, it is possible to also control the spectral response as well as the polarization state of the system. By composing a metasurface with such complex nanostructures fabricated in silver, we are able to control the scattered light and channel different colors into different directions. In the second series of experiments, we specifically study the multipolar radiation of a bianisotropic scatterer and use it for the efficient splitting of circularly polarized light, similar to a photonic spin Hall effect. Since the near-field enhancement and circularly polarized scattering in this case occur at the individual antenna level, this planar surface is capable of extracting the fluorescence and controlling the spin-polarized emission from nearby emitters, as will be demonstrated experimentally. These results have practical implications for controlling the optical activity and can potentially enable new polarization-dependent light-emitting devices for applications in imaging, optical communication, and optical displays.

Nanolasers with ultra-compact footprint are able to provide high intensity coherent light, which have various potential applications in high capacity signal processing, biosensing, and sub-wavelength imaging. Among various nanolasers, those lasers with cavities surrounded with metals have shown to have superior light emission properties due to the surface plasmon effect providing better field confinement capability and allowing exotic light-matter interaction. In this talk, we report robust ultraviolet ZnO nanolaser by using silver (Ag) [1] and aluminum (Al) [2] to strongly shrink the mode volume. The nanolasers operated at room temperature and even high temperature (353K) shows several distinct features including an extremely small mode volume, large Purcell factor and group index. Comparison of characteristics between Ag- and Al-based will also be made.

The ability to control the amplitude, phase and polarization states of light on subwavelength scales established metasurfaces as miniaturized alternatives to standard, the relatively large optical components. So far, most of these ultrathin elements operate in the linear regime, and do not change the frequency of the light transmitted or reflected from them. Using our better control over the response of the metasurfaces, we demonstrate a special class of metasurfaces that act as frequency-converting optical components [1-3]. Through nonlinear generation, plasmonic meta-atoms are used as the metasurfaces’ building blocks and a 2π phase shift can be imparted on the nonlinear wave. Similar to the linear metasurfaces case, the laws governing nonlinear optics can be generalized to include nonlinear phase gradients. In phase matched interactions for example, the anomalous signal generated in a collinear wave mixing scheme is emitted into another direction [2]. We demonstrate optical elements such as blazed gratings and lenses operating through four-wave mixing and third-harmonic generation. Additionally, we devise a novel type of computer-generated hologram that can reconstruct complex images at the third harmonic frequency of the reading beam [3]. Polarization-multiplexed, three-dimensional and dynamical nonlinear holograms are fabricated in ultrathin elements by multilayer nanolithography, paving the way to a class of devices that can manipulate optical beams in unprecedented ways. [1] E. Almeida and Y. Prior. Scientific Reports 5, 10033 (2015) [2] E. Almeida, G. Shalem and Y. Prior, Nature Communications 7, 10367 (2016) [3] E. Almeida, O. Bitton and Y. Prior, Nature Communications 7, 12533 (2016)

A stack of five layers of epitaxial InAs QDs with GaAs barriers was grown by molecular-beam epitaxy. The upper layer of QDs was capped by 3nm-GaAs/3nm-AlAs/4nm-GaAs layer sequence. Then, a thin silver layer was added via physical vapor deposition. After annealing isolated silver nanoparticles were formed above the layer of buried InAs quantum dots. We studied interplay of the exciton resonance in InAs QDs and plasmon resonance in Ag nanoparticles. In particular, we observed more than twofold enhancement of the exciton photoluminescence intensity from the InAs QDs when they were coupled to the silver nanoparticles.

Resolving the various interactions of lipids and proteins in the plasma membrane of living cells with high spatiotemporal resolution is of upmost interest [1]. Here we introduce an innovative design of plasmonic nanogap antennas to monitor single-molecule events on model biological membranes at physiological relevant concentrations by means of fluorescence correlation spectroscopy. Our design involves the fabrication of in-plane plasmonic nanogap antennas arrays embedded in nanometric-size boxes to provide full surface accessibility of the hotspot-confined region. Using these antennas we recently reported fluorescence enhancement factors of 104-105 times on individual molecules diffusing in solution, together with nanoscale detection volumes in the zeptoliter range [2]. In principle, the planarity of these antennas should enable similar studies on biological membranes without unwanted membrane curvature effects. To show their applicability, we recorded the diffusion of individual molecules inserted in multi-component lipid bilayers as a simple mimetic system that recapitulates some of the most important features of cell membranes. We prepared membranes of different compositions: saturated phospholipids, sphingolipids and cholesterol and used antennas of different gap sizes (10-45 nm). The diffusion of individual molecules on membranes consisting of phospholipids and/or in a mixture with sphingolipids resulted Brownian, confirming homogenous lipid distribution. Interestingly, the strong confinement of antennas revealed the formation of transient (<1ms lifetime) nanoscopic domains of ~11 nm in size upon cholesterol addition. These results indicate that in-plane antennas represent a highly promising non-invasive tool to investigate the nanoscale dynamic organization of biological membranes and its impact in biological function. References: [1] D. Lingwood, K. Simons, Science 327, 46 (2010). [2] V. Flauraud et al, submitted.

UV plasmonic nanostructures have applications in label free native fluorescence biosensing. Many aluminum nanostructures have been shown to modify emission properties of UV fluorescence molecules. However, these structures demonstrate small rate enhancement factors (less than 10x). In this paper, we report FDTD simulation results on excitation and emission enhancement factors of a pair of aluminum bowtie antenna in ultraviolet region. Our results show that the optimal geometry is a pair of small bowtie (radius 20nm) with apex angle 60 degrees. The highest radiative enhancement is 25x (~340nm) and highest total decay rate enhancement is 70x, higher than previously studied geometries.

Metallic nanostructure can enhance fluorescence through excited surface plasmons which increase the local field as well as improve its quantum efficiency. When coupling to cavity resonance with proper gap dimension, gap hot spots can be generated to interact with fluorescence at their excitation/emission region in UV. A 3D nano-cavity antenna array in Aluminum has been conducted to generate local hot spot resonant at fluorescence emission resonance. Giant field enhancement has been achieved through coupling fundamental resonance modes of nanocavity into surface plasmons polaritons (SPPs). In this work, two distinct plasmonic structure of 3D resonant cavity nanoantenna has been studied and its plasmonic response has been scaled down to the UV regime through finite-difference-time-domain (FDTD) method. Two different strategies for antenna fabrication will be conducted to obtain D-coupled Dots-on-Pillar Antenna array (D2PA) through Focus Ion Beam (FIB) and Cap- Hole Pair Antenna array (CHPA) through nanosphere template lithography (NTL). With proper optimization of the structures, D2PA and CHPA square array with 280nm pitch have achieved distinct enhancement at fluorophore emission wavelength 350nm and excitation wavelength 280nm simultaneously. Maximum field enhancement can reach 20 and 65 fold in the gap of D2PA and CHPA when light incident from substrate, which is expected to greatly enhance fluorescent quantum efficiency that will be confirmed in fluorescence lifetime measurement.

In this work, we theoretically investigate optical bistability and optical response of a hybrid system consisting of semiconductor quantum dot (SQD) coupled with a vanadium dioxide nanoparticle (VO₂NP) in the infrared (IR) regime. The VO₂ material exists in semiconductor and metallic phases below and above the critical temperature, respectively where the particle optical properties dramatically change during this phase transition. In our calculations a filling fraction factor controls the VO₂NP phase transition when the hybrid system interacts with a laser field. We demonstrate that the switch-up threshold for optical bistability is strongly controlled by filling fraction without changing the structure of the hybrid system. Also, it is shown that, the threshold of optical bistability increases when the VO₂NP phases changes from semiconductor to metallic phase. The presented results have the potential to be applied in designing optical switching and optical storage.

Light-matter interactions in two dimensional (2D) materials have given new momentum to nano optoelectronics since the observation of localized surface plasmons interacting with the excitons. Graphene, a typical metallic 2D crystal with high optical absorbance, can provide surface plasmon effects to proximate molecules as nanostructured metals do. The spontaneous emission rate can be enhanced by the coupling of plasmonic modes with the emission frequencies of organic molecules. However, most experimental and theoretical studies report graphene plasmonics in the terahertz to mid-infrared range. Here, we demonstrate the optical transition and significant amplification of singlet emission from phosphoric molecule on a graphene substrate, with simultaneous enhancement of triplet emission in the visible regime. The spectroscopic investigations ascribe these phenomena to the coupling of graphene plasmonic modes with molecular transient dipole. The modulation of emission channel and quantum efficiency is achieved by specifically controlling the organic molecular surface density on graphene. The single layer graphene is the most efficient substrate for plasmon coupling, however, remarkable strong PL intensity is achieved by forming multi-stacks of the organic molecule-graphene hybrid layer. This work suggests a novel route for the manipulation of organic molecular emissions using graphene plasmonics, and can be applied in developing photonic devices with high quantum efficiency.

Tunable UV devices can enable enhanced functionalities such as multiplexed sensing, wavelength-tunable light emission and so on. Interestingly, in the UV range, graphene shows a tunable optical absorption due to pi-plasmon resonance. In this work we study the UV transmission through monolayer graphene films transferred on top of aluminum hole-arrays. Transmittance though the hole-array was measured before and after graphene transfer. Interaction of graphene pi-plasmons with surface plasmon resonances leads to strong wavelength shifts, i.e. the surface plasmon resonance at the top-interface red-shifts when graphene is added. Furthermore, it is observed that maximum shift occurs in the 280 to 310 nm wavelength range. This is attributed to an enhanced graphene optical conductivity owed to pi-plasmons.

The fast development of nanoscience, especially in the field of nanoelectronics, nanophotonics and plasmonics, has shown a great demand for new nanofabrication techniques to fulfil diverse requirements. The nanolithographic methods, e.g conventional photolithography, focused electron beams lithography (EBL), and focus ion beams (FIB), all exhibit the capability for nanostructure fabrication but most of them inherently suffer from their nature, which limit the size of nanostructures, fabrication area, and throughput at reasonable costs. The limitations of these conventional lithographic techniques have motivated the development of alternative approaches such as micro-contact printing, scanning probe lithography and nanoimprinting lithography (NIL). In this paper, we propose a new alternative laser based approach which could satisfy the requirements of high resolution, fast processing speed for large area fabrication of sub-wavelength nanohole and nanoparticle arrays with feature size controllably varied from a few tens to a few hundreds nanometers. The technique, named as plasmonic nanoparticle lithography, effectively combines the laser induced transfer (LIT) [1, 2] and light-induced near-field nanomodification [3, 4] relying on the optical enhancement and thermal effect in near-field under spherical plasmonic nanoparticles. It allows producing ordered sub-wavelength nanohole arrays in a thin mask layer (e.g. Chromium film) upon laser exposure. Subsequent post-processing allows transferring the nanohole array into a desired substrate or converting it into an array of pillars made out of a desired material. References: 1. A. I. Kuznetsov, A. B. Evlyukhin, M. R. Gonçalves, C. Reinhardt, A. Koroleva, M. L. Arnedillo, R. Kiyan, O. Marti, and B. N. Chichkov, “Laser fabrication of large-scale nanoparticle arrays for sensing applications”, ACS Nano., 5(6),4843-9 (2011). 2. A. I. Kuznetsov, R. Kiyan, and B. N. Chichkov, "Laser fabrication of 2D and 3D metal nanoparticle structures and arrays", Optics Express, 18(20), 21198-21203 (2010). 3. P. G. Kika, S. A. Maiera and H. A. Atwater, Plasmon Printing - a New Approach to Near-Field Lithography, 2001 MRS Fall Meeting, MRS Proceedings, Volume 705 (2001). 4. A. Plech, V. Kotaidis, M. Lorenc and J. Boneberg, “Femtosecond laser near-field ablation from gold nanoparticles”, Nature Physics, 2, 44- 47 (2006).

Colloidal self-assembly combined with templated surfaces holds the promise of fabricating large area devices in a low cost facile manner. This directed assembly approach improves the complexity of assemblies that can be achieved with self-assembly while maintaining advantages of molecular scale control. In this work, electrokinetic driving forces, i.e., electrohydrodynamic flow, are paired with chemical crosslinking between colloidal particles to form close-packed plasmonic metamolecules. This method addresses challenges of obtaining uniformity in nanostructure geometry and nanometer scale gap spacings in structures. Electrohydrodynamic flows yield robust driving forces between the template and nanoparticles as well as between nanoparticles on the surface promoting the assembly of close-packed metamolecules. Here, electron beam lithography defined Au pillars are used as seed structures that generate electrohydrodynamic flows. Chemical crosslinking between Au surfaces enables molecular control over gap spacings between nanoparticles and Au pillars. An as-fabricated structure is analyzed via full wave electromagnetic simulations and shown to produce large magnetic field enhancements on the order of 3.5 at optical frequencies. This novel method for directed self-assembly demonstrates the synergy between colloidal driving forces and chemical crosslinking for the fabrication of plasmonic metamolecules with unique electromagnetic properties.

Optical metasurfaces are regular quasi-planar nanopatterns that can apply diverse spatial and spectral transformations to light waves. A critical challenge is to realize a technique of tuning their optical properties that is both fast and efficient. We will overview our recent results on controlling the properties of semiconductor-based metasurfaces with femtosecond laser pulses. Starting from silicon metasurfaces, where the instantaneous effect of two-photon absorption can be utilized to show all-optical switching as fast as 65 fs, we will show how direct-gap semiconductors can enable extremely nonlinear metasurfaces. In particular, it is experimentally shown that magnetic dipole resonances of GaAs nanoresonators can be tuned by almost full width at half maximum by ultrafast injection and relaxation of free carriers. We will also show that dynamic epsilon-near-zero and plasmonic regimes can be realized at longer wavelengths, making a smooth transition between plasmonic and all-dielectric metasurfaces.

Plasmons provide excellent sensitivity to detect analyte molecules through their strong interaction with the dielectric environment. Plasmonic sensors based on noble metals are, however, limited by the spectral broadening of these excitations. Here we identify a new mechanism that reveals the presence of individual molecules through the radical changes that they produce in the plasmons of graphene nanoislands. An elementary charge or a weak permanent dipole carried by the molecule are shown to be sufficient to trigger observable modifications in the linear absorption spectra and the nonlinear response of the nanoislands. In particular, a strong second-harmonic signal, forbidden by symmetry in the unexposed graphene nanostructure, emerges due to a redistribution of conduction electrons produced by interaction with the molecule. These results pave the way toward ultrasensitive nonlinear detection of dipolar molecules and molecular radicals that is made possible by the extraordinary optoelectronic properties of graphene.

The realization of efficient high-harmonic generation (HHG) in solid-state systems is anticipated to pave the way for compact ultraviolet and ultrafast light sources, and to provide fundamental insight into quantum many-body electron motion [1-3]. Here we argue that the large light intensity required for HHG to occur can be reached by exploiting localized plasmons in doped graphene nanostructures. In particular, we demonstrate that the synergistic combination of strong plasmonic near-field enhancement and a large intrinsic nonlinearity originating from the anharmonic charge-carrier dispersion of graphene result in efficient broadband high-harmonic generation within a single material [4]. We extract this conclusion from rigorous time-domain simulations using complementary nonperturbative approaches based on atomistic one-electron density matrix and massless Dirac-fermion Bloch-equation pictures, where the latter treatment is supplemented by a classical electromagnetic description of the plasmonic near-field enhancement produced by the illuminated nanostructure. High harmonics are predicted to be emitted with unprecedentedly large intensity by tuning the incident light to the localized plasmon resonances of ribbons and finite islands, which in turn can be actively modulated via electrical gating. In contrast to HHG in atomic systems, we observe no cutoff in harmonic order, while a comparison of graphene plasmon-assisted HHG to recent measurements in solid-state systems suggests that the HHG yields from bulk semiconductors can be produced by graphene plasmons using 3-4 orders of magnitude lower pulse fluence. Our results support the strong potential of nanostructured graphene as a robust, electrically-tunable platform for HHG.

Colloidal suspensions offer as a promising platform for engineering polarizibilities and realization of large and tunable nonlinearities. Previous studies of Gaussian beams propagation in various colloidal suspensions predicted in a number of remarkable optical phenomena and applications, including initiation and regulation of chemical reactions, sorting different species of nanoparticles and imaging through highly scattering media. As compared to the conventionally used Gaussian beams, optical vortices that are characterized by the doughnut-shaped intensity profile and a helical phase front offer even more degrees of freedom for, in particular, optical trapping or imaging applications. In our earlier work, we predicted, using the linear stability analysis and numerical simulations, that the perturbations with an orbital angular momentum of a particular charge will be amplified and lead to the formation of a necklace beam with a particular number of peaks, or “beads.” Here, we performed detailed experimental studies of such necklace beam formation that show an excellent agreement with the analytical and numerical predictions. This work might bring about new possibilities for dynamic optical manipulation and transmission of light through scattering media as well as formation of complex optical patters in colloids.

Natural toroidal molecules, such as biomolecules and proteins, possess toroidal dipole moments that are hard to be detected, which leads to extensive studies of artificial toroidal materials. Recently, toroidal metamaterials have been widely investigated to enhance toroidal dipole moments while the other multipoles are eliminated due to the spacial symmetry. In this talk, we will show several cases on the plasmonic toroidal excitation by engineering the near-field coupling between metamaterials, including their promising applications. In addition, a novel design for a toroidal metamaterial with engineering anapole mode will also be discussed.

In this talk, I introduce two plasmonic devices. Firstly, we design and construct a three-dimensional (3D) negative index medium (NIM) composed of gold hemispherical shells to supplant an integration of a split-ring resonator and a discrete plasmonic wire for both negative permeability and permittivity at THz gap. With the proposed highly symmetric gold hemispherical shells, the negative index is preserved at multiple incident angles ranging from 0° to 85° for both TE and TM waves, which is further evidenced by negative phase flows in animated field distributions and outweighs conventional fishnet structures with operating frequency shifts when varying incident angles. Finally, the fabrication of the gold hemispherical shells is facilitated via standard UV lithographic and isotropic wet etching processes and characterized by -FTIR. The measurement results agree the simulated ones very well. Secondly, we present a miniature surface plasmon polariton amplitude modulator (SPPAM) by directing and interfering surface plasmon polaritons on a nanofabricated chip. Our results show that this SPPAM enables two kinds of modulations. The first kind of modulation is controlled by encoding angular-frequency difference from a Zeeman laser, with a beat frequency of 1.66 MHz; the second of modulation is validated by periodically varying the polarization states from a polarization generator, with rotation frequencies of 0.5-10k Hz. In addition, the normalized extinction ratio of our plasmonic structure reaches 100. Such miniaturized beat-frequency and polarization-controlled amplitude modulators open an avenue for the exploration of ultrasensitive nanosensors, nanocircuits, and other integrated nanophotonic devices.

Increasing the nonlinear optical response at nanometer length scale is a very important issue due to the wide applications in various disciplines such as information science, bio-medicine and quantum computation technology. Second harmonic generation (SHG) arising from the metal nanostructures has provide a very powerful tool in studying the surface and interface properties of these materials. The SHG from various kinds of asymmetric geometric configurations such as V and L shape structures, imperfect nano-spheres, metal/insulator/metal multilayer structures, and planar split ring resonators have been proposed. However, all the previous studies in plasmonic nonlinear optical behavior rely on the enhancement of the electric field and seldom considered the magnetic field effect. In this work, we present a vertical split ring resonator (SRR) based metamaterial to generate SHG. By adopting such a novel structure, both the electric and magnetic field will be significantly enhanced due to the localized surface plasmon resonance, hence the generation of the second-harmonic and its re-emission into the far field are dramatically increased several orders comparing with that of the planar SRR. We simulated and fabricated the reflective type vertical SRR, and optimized the aspect ratio to maximize the SHG signal. We further systematically studied the nonlinear optical response in the vertical SRR dimers and trimers and found that the gap distance between two SRRs plays a very important role in the SHG intensity. This work paves a new way in increasing the nonlinear transition quantum efficiency and provides a new insight in designing new nonlinear sources.

We proposed an unbalanced Mach-Zehnder interferometer (MZI) by using Metal/Insulator/Metal PWGs for optical modulation or sensor devises. Transmission spectra of the MZI were calculated by Finite difference time domain method. We observed an interference pattern and transmission dips in calculated transmission spectra of an unbalanced MZI. An interference pattern is due to different path length of an unbalanced MZI. The Transmission dips are due to resonance in unbalanced MZI. Standing wave was appeared when the wavelength of the gap plasmon mode is equal to the integral multiple of PWG length of resonance area. Therefore, an unbalanced MZI in plasmonic waveguides serves as a ring resonator.

We present the results of numerical simulations and preliminary experiments to investigate the nano-focusing effect of incident light based on the surface plasmon polaritons (SPPs) on the nano-metallic-planar-apex metamaterials (NMPAM). The NMPAM are prepared by Focused Ion Beam lithography (FIB), a nanoscale fabrication tool. The NMPAM can be used to remarkably enhance the strength of the surface evanescent and lead to the excitation of several SPP modes on the metal surface. The interaction of different SPPs result in unique near-field optical properties for imaging and optical storage, so as to focus light into a nano-size point and thus enhance the light power greatly. The energy flow and electromagnetic field distribution is calculated by finite-difference time-domain (FDTD) method. The nano-spot position and intensity is experimentally shown to be controlled by the array of the apex. In our experiments, we fabricate a 10×10 array by FIB, and then the scanning near-field optical microscopy (SNOM) is used to observe the optical power distribution in nano-scale at the air-metal interface in the infrared region. we find that the light can be focus into ~100nm-scale and consequently enhance the light power up to several times than before common focusing method. The principle of nano-focusing based on nano-planar-apex is theoretically explained. The NMPAM can be utilized for coupling with infrared pixels to enhance the incident light converging so as to improve signal to noise ratio of infrared detection.

Mobile communications have massively populated the consumer electronics market over the past few years and it is now ubiquitous, providing a timeless opportunity for the development of smartphone-based technologies as point-of-care (POC) diagnosis tools¹ . The expectation for a fully integrated smartphone-based sensor that enables applications such as environmental monitoring, explosive detection and biomedical analysis has increased among the scientific community in the past few years^2,3. The commercialization forecast for smartphone-based sensing technologies is very promising, but reliable, miniature and cost-effective sensing platforms that can adapt to portable electronics in still under development. In this work, we present an integrated sensing platform based on flow-through metallic nanohole arrays. The nanohole arrays are 260 nm in diameter and 520 nm in pitch, fabricated using Focused Ion Beam (FIB) lithography. A white LED resembling a smartphone flash LED serves as light source to excite surface plasmons and the signal is recorded via a Complementary Metal-Oxide-Semiconductor (CMOS) module. The sensing abilities of the integrated sensing platform is demonstrated for the detection of (i) changes in bulk refractive index (RI), (ii) real-time monitoring of surface modification by receptor-analyte system of streptavidin-biotin.

A method for development of gratings for effective excitation of surface plasmonic waves using holography principles has been proposed and theoretically analyzed. The case of excitation of a plasmonic wave in a dielectric layer on metal using volume holograms in the dielectric layer has been considered. For comparison, simple periodic gratings with refractive index of the dielectric layer modulated in the plane of the layer and invariable in the direction perpendicular to the layer plane have been considered. The efficiencies of the proposed holograms and gratings optimized for various incidence angles of exciting waves incident on the gratings/holograms from air have been analyzed. Based on this analysis, general enough conditions when holograms can be more efficient than simple gratings have been found out. In particular, a hologram is expected to be more efficient than the grating when the refractive index distribution in the hologram is considerably inhomogeneous (contrary to the gratings) in the direction perpendicular to the layer plane. For example, this may be the case if the exciting wave is incident on a hologram obliquely at a rather large angle or if phase fronts of either exciting wave or a wave being excited are curved. The proposed holographic method is quite universal. As expected, this can be extended for efficient excitation of different types of optical surface waves and modes of optical waveguides.

In this project we develop a handheld, portable, highly selective and sensitive chem/biosensor that has potential applications in both airborne and water-based environmental sensing. The device relies on a plasmonic chip of subwavelength-scale periodic gold rods engineered to resonate in the near infrared. The chip is functionalized with a novel class of proteins that exhibit large conformational changes upon binding to a specific target analyte. The subsequent change in local refractive index near the surface of the gold is one to two orders of magnitude greater than current conventional methods, which produces a readily measurable 5 to 10 percent difference in light transmission. This allows us to forgo traditional, bulky tabletop setups in favor of a compact form factor. Using commercially available optics to construct a transmission-based optical train, measured changes in bulk refractive index are presented here. While synthesis of binding protein efforts are focused on heme as analyte for proof of concept validation, the functionalized protein can be engineered to pair with a wide variety of analytes with minimal alterations to the plasmonic chip or device design. Such flexibility allows for this device to potentially meet the needs of first responders and health care professionals in a multitude of scenarios.

In this paper, a novel metallic nanostructure consisting of two rings with different diameter is proposed to generate intense plasmonic Fano Resonances (FRs). In this nanostructure, the FRs is explained by the interference between spectrally overlapping narrow subradiant (dark) and broad superradiant (bright) plasmonic modes and is simulated by COMSOL Multiphysics based on Finite Element Method. The simulation shows that dipolar resonance only occurs in the small-diameter ring as a bright plasmon mode, other than the large-diameter ring. It can be found that the Fano resonance can be generated in a metallic nanostructure consisting of two rings with different diameter. Such structure will have many potential applications in the field of chemical and biological sensors in the future.

In this paper, we theoretically demonstrate a polarizing filter consisted of graphene ribbon arrays with varying width placed on the top surface of dielectric and a metal reflector rested at the bottom of the structure. It is found that proper ribbon width, which corresponds to resonant frequency of graphene plasmons, is a crucial factor that can significantly influence the absorption effect. The results of fullwave numerical simulations indicate that total absorption of more than 90% for TE polarization and approaching to 1% for TM polarization can be achieved at normal incidence in the infrared range. Therefore, this characteristic can be applied into polarizing filter by adjusting the coupling effect between the graphene ribbon arrays. Such structure will be beneficial to the manufacture of infrared nano-photonic devices for optical filtering and selective absorption.

In this paper, a design of Plasmonic waveguides based optical AND gate has been proposed. Various designs of Photonic crystal based optical logic gates have already been envisioned and proposed during the past decade, in which, wavelength of operation is comparable to the geometrical parameters. On the contrary, the proposed structure consists of Plasmonic waveguides whose thickness is much smaller than the wavelength of operation. Plasmonics can pave way for the development of optical interconnects that are small enough to operate in nanoscale devices. Nowadays, Plasmonics is being implemented in a large number of areas, one of which is confinement of optical power in subwavelength devices. This may pave the way for large scale on-chip integration for the development of all optical circuits for optical computing systems. Moreover, the proposed design is simple and easy to fabricate using techniques like thin-film technology and lithography. This AND gate has been designed and analysed using the Finite Element Method (FEM) software. The proposed structure has been made by using silver material as a waveguide and silicon as the surrounding dielectric..

A multipeak polarization independent absorber based on ultrathin metamaterials composed of metal layers (Al) and dielectric (polymer, ZnSe) has been proposed and numerically analyzed. The absorber is composed by a trapezoidal shaped grating filled by a polymer. This structure possess resonant absorption modes at multi-frequencies. Numerical results show that near unity absorption peaks can be obtained for both polarization modes (TM and TE) for visible radiation at normal incidence.

The paper presents second harmonic generations (SHG) from Au nanoprisms at localized surface plasmon resonances. The model system was equilateral triangular nanoprisms that were arranged two-dimensionally in trigonal lattices. At lower excitation power regions, the SHG conversion efficiencies were almost independent of the excitation light polarization angles, while the polarization angles of the SHG waves were twice as much as those of the excitation light polarizations. The polarization dependencies were in a good agreement with the demands required from the C3v point symmetry of the systems. On the other hand, the SHG conversion efficiencies were dependent on the excitation light polarization angles at higher excitation power regions. The anisotropy in the nonlinear optical responses was explained from the viewpoint of the polarization-dependent depletions of the surface electrons on the metal surfaces.

Efficient directional couplers composed by parallel dielectric and metallic waveguides have been analyzed in details. The results show that an efficient power conversion of optical dielectric modes to long range plasmonic ones is possible in such devices. Low insertion losses in conjunction with short coupling length as well as a broadband operation can be obtained under certain conditions. This kind of couplers has potential applications for the design of photonic integrated circuits and for signal routing between dielectric and plasmonic waveguides.

The directional dependency of the optical coefficients, such as absorbance and reflectance, of a periodic hole plasmonic structure is numerically simulated and investigated. The tridimensional structure, which is composed of a metallic thin layer on a semiconductor matrix, is polarization independent and exhibits wide angle tolerance. It is found that the optical coefficients of the simulated structure have strong dependency to the radii of the holes due to cavity modes resonance and surface plasmon resonance. Simulations were carried out using gold and silver, varying the holes radii ranging from 40 to 70nm, as well as its depth, from 30 to 60nm of the metallic thin layer and from 100 to 200nm of the semiconductor matrix. A maximum contrast ratio of a unit was obtained. The resonant modes excited in the structure and excitation of surface plasmon polaritons in the metallic side illumination favors absorption, which explains the asymmetric behavior. We also investigate the structure’s fabrication sensitivity by randomizing the generation of center of the holes in a supercell. These findings are significant for a diverse range of applications, ranging from optical integrated circuits to solar and thermovoltaics energy harvesting.

We proposed and designed angle insensitive color filter based in metal/dielectric multilayers structures for red electromagnetic radiation (620-750nm). The thickness of the dielectric in the structure is calculated according to the physical theory and the omnidirectional resonance occurs when the reflection phase shift cancels the propagation displacement. The thickness of the metal is chosen analyzing a transmission properties in an interval of thicknesses previously described in the literature. We obtain analytically a highly stable filter with a transmission peak greater than 70% in approximately 634nm. This device can keep the same perceived transmitted color when the incidence angle changes from 0° to 50°, especially for TM polarized light.

This paper studies theoretically how the optics of multiple grooves in a metal change as the number of grooves is increased gradually from a single groove to infinitely many arranged in a periodic array. In the case of a single groove the out-of-plane scattering (OUP) cross section at resonance can significantly exceed the groove width. On the other hand a periodic array of identical grooves behaves radically different and is a near-perfect absorber at the same wavelength. When illuminating multiple grooves with a plane wave the OUP cross section is found to scale roughly linearly with the number of grooves and is comparable to the physical array width even for widths of many wavelengths. The normalized OUP cross section per groove even exceeds that of a single groove, which is explained as a consequence of surface plasmon polaritons generated at one groove being scattered out-of-the-plane by other grooves. In the case of illuminating instead with a Gaussian beam, and observing the limit as the incident beam narrows and is confined within the multiple-groove array, it is found that the total reflectance becomes very low and that there is practically no out-of-plane scattering. The well-known result for periodic arrays is thus recovered. All calculations were carried out using Greens function surface integral equation methods taking advantage of the periodic nature of the structures. Both rectangular and tapered grooves are considered.

Nanoscale size effects bring additional near-field thermal considerations when heating nanoparticles under high laser power. Scanning electron micrographs of a typical copper nanoparticle powder bed reveal that the nanoparticles are distributed log-normally with 116 nm mean radius and 48 nm standard deviation. In this paper, we solve Maxwell’s equations in frequency domain to understand near-field thermal energy effects for different standard deviations. Log-normally distributed copper nanoparticle packings which have 116 nm mean radius with 3 different standard deviations (12, 48 and 84 nm) are created by using Discrete Element Model (DEM) in which certain number of particles are generated, specifying a position and radius for each. The solid particles interacting with the neighbouring particles are to be distributed randomly into the bed domain with an initial velocity and a boundary condition, which creates the particle packing within a defined time range under gravitational and weak van der Waals forces. Finite Difference Frequency Domain analysis, which yields the electromagnetic field distribution, is applied by solving Maxwell's equations to obtain absorption, scattering and extinction coefficients. We show that different particle distributions create different plasmonic effects in the bed domain which results in non-local heat transport. We calculate the surface plasmon effect due to the electromagnetic coupling between the nanoparticles and the dielectric medium under the different distributions. This analysis helps to reveal how sintering quality can be enhanced by creating stronger laser-particle interactions for specific groups of nanoparticles.

THz imaging has become a hot research topic in recent years, thanks to its merits of non-contact, strong penetration, immunity to hostile environments, and nondestructive detection. However, its spatial resolution is limited by the relatively long wavelength, so the location and measurement precision can only reach the level of the imaging wavelength, which has become a severe limitation of THz imaging. A simple way using surface plasmonic polartons (SPPs) to improve the location and measurement precision of THz by one order of magnitude was proposed in this manuscript, which can realize subwavelength THz imaging.

Orientation of plasmonic nanostructures is an important feature in many nanoscale applications such as catalyst, biosensors DNA interactions, protein detections, hotspot of surface enhanced Raman spectroscopy (SERS), and fluorescence resonant energy transfer (FRET) experiments. However, due to diffraction limit, it is challenging to obtain the exact orientation of the nanostructure using standard optical microscope. Hyperspectral Imaging Microscopy is a state-of-the-art visualization technology that combines modern optics with hyperspectral imaging and computer system to provide the identification and quantitative spectral analysis of nano- and microscale structures. In this work, initially we use transmitted dark field imaging technique to locate single nanoparticle on a glass substrate. Then we employ hyperspectral imaging technique at the same spot to investigate orientation of single nanoparticle. No special tagging or staining of nanoparticle has been done, as more likely required in traditional microscopy techniques. Different orientations have been identified by carefully understanding and calibrating shift in spectral response from each different orientations of similar sized nanoparticles. Wavelengths recorded are between 300 nm to 900 nm. The orientations measured by hyperspectral microscopy was validated using finite difference time domain (FDTD) electrodynamics calculations and scanning electron microscopy (SEM) analysis. The combination of high resolution nanometer-scale imaging techniques and the modern numerical modeling capacities thus enables a meaningful advance in our knowledge of manipulating and fabricating shaped nanostructures. This work will advance our understanding of the behavior of small nanoparticle clusters useful for sensing, nanomedicine, and surface sciences.

Surface plasmon waves carry an intrinsic transverse spin angular momentum, which is locked to their propagation direction. On the other hand, helical plasmonic distributions may also carry an orbital angular momentum that is linked to the field topology. Apparently, when such a singular plasmonic mode propagates on a surface or is guided on a conic structure its helicity and the transverse spin can be coupled to the far-field spin and orbital angular momentum. We discuss the mechaism of such a coupling by using 2D and 3D guiding architetures. We analyze the coupling efficiency in each case as well as the intriguing spin-locking phenomenon occurring in our system. Finally we experimentally demonstrate the efficient beaming of a single-handed mode decorated by a desired orbital angular using accurately fabricated nanostructures.

Plasmonic nanostructures are highly used for sensing purposes since they support plasmonic modes which make them highly sensitive to the refractive index change of their surrounding medium. Therefore, they can also be used to detect changes in optical properties of ultrathin layer films in a multilayer plasmonic structure. Here, we investigate the changes in optical properties of ultrathin films of macro structures consisting of STT-RAM layers. Among the highest sensitive plasmonic structures, nanohole array has attracted many research interest because of its ease of fabrication, small footprint, and simplified optical alignment. Hence it is more suitable for defect detection in STT-RAM geometries. Moreover, the periodic nanohole pattern in the nanohole array structure makes it possible to couple the light to the surface plasmon polariton (SPP) mode supported by the structure. To assess the radiation damages and defects in STT-RAM cells we have designed a multilayer nanohole array based on the layers used in STT-RAM structure, consisting 4nm- Ta/1.5nm-CoFeB/2nm-MgO/1.5nm-CoFeB/4nm-Ta layers, all on a 300nm silver layer on top of a PEC boundary. The nanoholes go through all the layers and become closed by the PEC boundary on one side. The dimensions of the designed nanoholes are 313nm depth, 350nm diameter, and 700nm period. Here, we consider the normal incidence of light and investigate zeroth-order reflection coefficient to observe the resonance. Our simulation results show that a 10% change in refractive index of the 2nm-thick MgO layer leads to about 122GHz shift in SPP resonance in reflection pattern.