This PDF file contains the front matter associated with SPIE Proceedings Volume 9163, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

A key challenge for the development of active plasmonic nanodevices is the lack of materials with fully controllable plasmonic properties. In this work, we demonstrate that a plasmonic resonance in top-down nanofabricated yttrium antennas can be completely and reversibly turned on and off using hydrogen exposure. We fabricate arrays of yttrium nanorods and optically observe in extinction spectra the hydrogen-induced phase transition between the metallic yttrium dihydride and the insulating trihydride. Whereas the yttrium dihydride nanostructures exhibit a pronounced particle plasmon resonance, the transition to yttrium trihydride leads to a complete vanishing of the resonant behavior. The plasmonic resonance in the dihydride state can be tuned over a wide wavelength range by simply varying the size of the nanostructures. Furthermore, we develop an analytical diffusion model to explain the temporal behaviour of the hydrogen loading and unloading process observed in our experiments and gain information about the thermodynamics of our device. Thus, our nanorod system serves as a versatile basic building block for active plasmonic devices ranging from switchable perfect absorbers to active local heating control elements.

This paper considers a range of plasmonic-black-metal polarizers suitable for ultra-short pulses. The polarizers consist of a metal surface being nanostructured with a periodic array of ultra-sharp grooves with periods of 250-350 nanometers, and groove depths around 500 nanometers. The surfaces can be designed such that practically all incident light with electric field perpendicular to the groove direction is absorbed. The efficient absorption is due to incident light being coupled into gap-plasmon polaritons that propagate downwards in the gaps between groove walls towards the groove bottom, where it is then subsequently absorbed during propagation. Reflection is largely avoided due to an adiabatic groove taper design. The other polarization, however, is very efficiently reflected, and the main point of this paper is that the reflection is with negligible dispersive stretching even for ultra-short pulses of 5-10 femtoseconds temporal width in the visible and near-infrared. Temporal pulse shapes after reflection are calculated by decomposing the incident laser pulse into its Fourier components, multiplying with the reflection coefficient in the frequency domain, and then Fouriertransforming the product back to the time-domain. Reflection of pulses is compared for polarizers based on different metals (gold, nickel, chromium). Polarizers are studied for two groove-array designs and two directions of light incidence, center wavelengths 650 nm and 800 nm, and pulse widths 5 fs and 10 fs for the incident pulse.

The simple source model used in the conventional finite difference time domain (FDTD) algorithm gives rise to large errors. Conventional second-order FDTD has large errors (order h**2/ 12), h = grid spacing), and the errors due to the source model further increase this error. Nonstandard (NS) FDTD, based on a superposition of second-order finite differences, has been demonstrated to give much higher accuracy than conventional FDTD for the sourceless wave equation and Maxwell’s equations (h**6 / 24192). Since the Green’s function for the wave equation in free space is known, we can compute the field due to a point source. This analytical solution is inserted into the NS finite difference (FD) model and the parameters of the source model are adjusted so that the FDTD solution matches the analytical one. To derive the scattered field source model, we use the NS-FD model of the total field and of the incident field to deduce the correct source model. We find that sources that generate a scattered field must be modeled differently from ones radiate into free space. We demonstrate the high accuracy of our source models by comparing with analytical solutions. This approach yields a significant improvement inaccuracy, especially for the scattered field, where we verified the results against Mie theory. The computation time and memory requirements are about the same as for conventional FDTD. We apply these developments to solve propagation problems in subwavelength structures.

We study strong coupling between plasmons in monolayer charge-doped graphene and excitons in a narrow gap semiconductor quantum well separated from graphene by a potential barrier. We show that the Coulomb interaction between excitons and plasmons result in mixed states described by a Hamiltonian similar to that for exciton-polaritons and derive the exciton-plasmon coupling constant that depends on system parameters. We calculate numerically the Rabi splitting of exciton-plasmariton dispersion branches for several semiconductor materials and find that it can reach values of up to 50 - 100 meV.

We here presents the first unified theory of the response of plasmonic nanoshells assisted by optical gain media. Our approach combines rigorous Mie scattering equations for the plasmonic structure and the density matrix formalism, which is well known in laser physics, allowing a correct description of different relaxation and energy exchange channels in the system. We derive a fundamental equation for calculation of SPASER frequency which we claim to be valid for any type of SPASER physical geometry. We demonstrate that ONLY radiative losses are responsible for the spasing and loss compensation process in the laser resonator.

We present the first experimental realization of an isotropic IR metamaterial using fourfold-symmetric 3D configuration of metallic nanostructures. Mass-productive formation of the assembled 3D stereostructures was achieved by a newly-developed metal-stress driven self-folding method. Systematic transmission spectroscopy demonstrated unambiguous isotropic characteristics for any lateral rotation, polarization, and incident angle up to 40º. The corresponding numerical simulations well re-produced the experimental results, revealing that the interplay of electric and magnetic interactions of the 3D metallic nanostructures plays a crucial role for the bi-anisotropic responses. Our results demonstrated a promising method to manufacture highly symmetric metamaterials, leading to isotropic optical responses.

Split ring resonator (SRR) has attracted wide attentions since the discovery of negative refraction in 2002. Here, we designed and fabricated vertical SRR (VSRR) arrays and toroidal metamolecule by using double exposure e-beam lithography with precise alignment technique, and their resonance behaviors are subsequently studied in optical region. The fundamental resonance properties of VSRR are studied as well as the plasmon coupling in a VSRR dimer structure by changing the gap distance between SRRs. In addition, we proposed a three-dimensional toroidal structure composed a VSRR with a dumbbell structure that supported a toroidal resonance under normal incidence with broadband working frequency. Such toroidal metamaterial confines effectively the electric as well as magnetic energy paving a way for promising applications in the field of plasmonics, such as integrated 3D plasmonic metamaterials, plasmonic biosensor and lasing spaser.

Plasmonic devices can be used to construct nanophotonic circuits and are very promising candidates for next-generation information technology. The functions of plasmonic circuits rely on the rigorous control of plasmon modes. Two different methods were proposed to control the propagation of surface plasmons (SPs) supported by Ag nanowires (NWs). The first one is modulating the beat period of the near-field distribution pattern, which can be realized by depositing Al₂O₃ layer or changing the refractive index of surrounding medium. The beat period increasing by 90 nm per nanometer of Al₂O₃ coating or by 16 μm per refractive index unit was obtained in experiments. The second one is introducing local structural symmetry breaking to realize mode conversion of SPs. Three typical structures including NW-nanoparticle (NP) structure, branched NW and bent NW were used to investigate the mode conversion. It’s revealed that the mode conversion is a scattering induced process. The lossy characteristic of SPs at optical frequencies typically limits the propagation length and hinders the further development of integrated plasmonic circuits. CdSe nanobelt/Al₂O₃/Ag film hybrid plasmonic waveguide was proposed to compensate the loss of SPs by using an optical pump-probe technique. Compared to the measured internal gain, the propagation loss was almost fully compensated for the TM mode. These results for mode control and loss compensation of propagating SPs are important for constructing functional nanophotonic circuits.

Using conventional wire grid polarizers to manipulate the polarization of deep ultraviolet (DUV) light is generally known as difficult because of the limits of the current nano-fabrication technologies. To ease the fabrication, two metallic gratings, Al-air and Al-SiO₂ gratings, with periods slightly smaller than the DUV wavelength, were designed to exhibit an inverse polarizing effect, i. e. with TE transmittance largely exceeding TM transmittance. Both gratings were experimentally verified to possess inverse polarization transmission, whereas an enhanced TE transmission through Al- SiO₂ grating was observed. By using the Fourier modal method and the planar waveguide theory, we show that the strong coupling of the incident DUV wave to surface plasmons results in the minimum in TM transmittance, whereas the coupling to low-loss TE mode leads to the TE transmission through the grating region. By conformally filling the grating slits with the substrate dielectrics-SiO₂, the effective refractive index of the TE guided mode approaching that of the substrate greatly reduces the reflection of the mode at the grating-substrate interface. Thus, the TE transmittance of Al- SiO₂ grating is largely enhanced compared with Al-air case. At the DUV lithographic wavelength-193 nm, the measured inverse polarization extinction ratio of Al-SiO₂ grating is 103, suggesting itself a qualified compact polarizer for ArF 193 nm lithography system.

We report our recent development in pursuing high Quality-Factor (high-Q factor) plasmonic resonances, with vertically aligned two dimensional (2-D) periodic nanorod arrays. The 2-D vertically aligned nano-antenna array can have high-Q resonances varying arbitrarily from near infrared to terahertz regime, as the antenna resonances of the nanorod are highly tunable through material properties, the length of the nanorod, and the orthogonal polarization direction with respect to the lattice surface,. The high-Q in combination with the small optical mode volume gives a very high Purcell factor, which could potentially be applied to various enhanced nonlinear photonics or optoelectronic devices. The 'hot spots' around the nanorods can be easily harvested as no index-matching is necessary. The resonances maintain their high-Q factor with the change of the environmental refractive index, which is of great interest for molecular sensing.

A detailed comparison of third-order nonlinear optical properties of colloidal gold nanoshells (NSs) and gold nanorods (NRs) in water solutions has been carried out with the open- and closed-aperture Z-scan measurements, performed with femtosecond laser pulses over a broad range of wavelengths. Absorption saturation was found to be a dominant effect for all the studied nanoparticles, however two-photon absorption properties are also detected, especially at the shortest wavelengths studied. The value of the merit factor σ₂/M (two-photon absorption cross section scaled by the molecular weight) for the NRs (10nm × 35 nm) at 530 nm is 7.5 (GM·mol/g), while for the NSs is 1.9 (GM·mol/g) at the same wavelength.

In this work we propose and study a highly sensitive quantum dot (QD)-metal film plasmonic composite. The system comprises of indium arsenide (InAs) QDs on silver film. The intensity is traced by scanning the absorption spectra for the system. We found that the behaviour of the plasmonic composite changes by varying the thickness of metal film. It is observed that the sensitivity of the composite varies with the thickness of metallic film and the quantum size effects dominate at sub-nanometer gap. The proposed system shows promising applications in lasing, sensing and spectroscopy.

We report the first experimental demonstration of plasmon-exciton coupling between silver nanowire (NW) and a pair of quantum dots (QDs). The resolving of single surface plasmons (SPs) generated in the NW-QD pair system is achieved. The accurate positions of the two QDs and NW ends are obtained by using a maximum likelihood single molecule localization method, and the separation distances between the two QDs range from microns to 200 nm within the diffraction limit. Parameters including the SP propagation length and the wire terminal reflectivity are experimentally determined and taken into account. The efficiency of plasmon generation due to the exciton-plasmon coupling is obtained for each QD.

In this review we discuss the evolution of surface plasmon resonance and localized surface plasmon resonance based hydrogen sensors. We put particular focus on how they are used to study metal-hydrogen interactions at the nanoscale, both at the ensemble and the single nanoparticle level. Such efforts are motivated by a fundamental interest in understanding the role of nanosizing on metal hydride formation processes. However, nanoplasmonic hydrogen sensors are not only of academic interest but may also find more practical use as all-optical gas detectors in industrial and medical applications, as well in a future hydrogen economy, where hydrogen is used as a carbon free energy carrier.

Our experiments demonstrate ultrahigh resolution imaging of localized plasmonic fields with a scanning tunneling microscope (STM). Plasmons are optically excited on gold nanoplasmonic antennas, and the fields localize in the nanometer scale voids and chasms between the gold grain boundaries. The plasmon field manifests in the nonlinear tunneling junction as a rectified tunnel current signal, which can be analyzed to produce maps of the plasmon field localization with an unprecedented resolution of 1nm. The experimentally observed signals are conclusively attributed to the plasmon excitation. Extensions of this procedure have the potential to produce plasmonic field distribution maps with angstrom resolution.

Controlled deposition of metal nanostructures on various substrates is highly desirable for electronics, photonics, sensing and catalysis. A laser focused beam has been used to deposit metal nanoparticles and nanostructures based on optical forces with diffraction-limited spatial resolution. We demonstrate fabrication of nanostructured silver wires, spots and wire arrays by using a confocal microscope setup, offering highly reproducible nanostructured silver growth and pattern writing. Particularly, laser-deposited silver micro-wires show adjustable electronic conductivities. Taking into accounts the superior spatial resolution and versatile pattern design, this technique is promising for a variety of applications such as microelectronics and bio-chips.

Metallic nanostructures such as gratings or antennas operate as a coupling structure that couples incident light to surface plasmon polaritons (SPPs) propagating thereon or on an underlying thin metal film. When deposited on a semiconductor such as a Si substrate the nanostructures become useful as infrared intensity modulators or photodetectors, exploiting SPP-enhanced carrier refraction in Si, or SPP-enhanced internal photoemission, respectively. Various materials are considered, including materials that are standard for electronics.

3D-electromagnetic (EM) analysis of surface plasmon polaritons (SPPs) excited by a single-mode (SM) propagation of visible lightwave in an optical fiber has been studied with a 3D-FEM package based on a finite element method. End of the fiber is formed to be a circular cone by wet etching process, and is FIBed to make a circular truncated conical shape with a flat circular surface a few micrometers in diameter. The flat end is covered with three layers of asymmetric metalinsulator- metal structure, thin metallic layer (M1), thick insulator layer (I), and thick metallic layer (M2), respectively. The outermost M2 layer has FIBed nanoholes to convert light waves at the extremity of the fiber into SPPs efficiently, and a bright tiny point light source will be generated on the surface of the M2 layer. In this study, the 3D-FEM models consists of both the MIM structure and the shrinking optical fiber tip coated with a metallic thin film has been designed and analyzed numerically. By applying perfect electric conductor and perfect magnetic conductor to planes containing the axis of rotation, the FEM model has a quarter of the circular truncated conical shape. The FEM analysis is formed in two steps. At the first step, a FEM mode analysis is performed to obtain a solution corresponding to the SM propagation in the fiber. The second level of action is the FEM analysis of EM field in the whole of model to find a stationary solution with the solution of mode analysis. Characteristic of wavelength-dependent excitation, propagation, and focusing of the SPPs will be presented with several experimental results of trial products of the fiber tip.

Plasmonic structures can be used to enhance electromagnetic radiation, and nanoscale (<5 nm) gaps can increase this enhancement even further. Fabrication of these desired structures involves using a relatively new, previously developed self-aligned process to overcome typical electron beam lithography resolution limits. The resulting nanogap structures have been shown to exhibit enhanced optical emission. This technique enables the fabrication of a large-area two-dimensional matrix of such nanostructures which could prove useful for photovoltaics, plasmonically enhanced Raman spectroscopy, biosensing, and other optoelectronic applications. Computational electromagnetic simulations of the structures will prove useful for predicting behavior upon interaction with light and for experimental comparison.

Heat generation in plasmonic nanostructures has attracted enormous attention due to the ability of these nanostructures to generate high temperatures in nanoscale volumes using far-field irradiation, enabling applications ranging from photothermal therapy to fast (sub-nanosecond) thermal optical switching. Here we investigate the optical and thermal response of a heterogeneous trimer structure composed of a gold nanoparticle surrounded by two larger silver nanoparticles analytically and numerically. We observe that this type of multi-scale multi-material plasmonic oligomer can produce temperature changes over two orders of magnitude higher than possible with isolated gold nanoparticles.

Photolithography is widely used to transfer a geometric pattern from a mask to a photoresist film, but the minimum feature sizes are limited by diffraction through the mask. Focused ion beam and electron beam lithography can be used when higher resolution is desired, but the write times are long and costly. Deep ultraviolet interference lithography, which is a maskless technique, can be used as an alternative to produce high resolution patterns with feature sizes as small as 100 nm. Since double negative metamaterial superlenses can be used for super-resolving and imaging subwavelength objects, there is a need for fabricating such objects to characterize the performance of these metamaterials. In this paper, simulations using standard finite element methods are first used to verify super-resolution and near-field imaging at 405 nm for such objects using a metamaterial superlens previously fabricated from silver and silicon carbide nanoparticles. Thereafter, results of fabrication and characterization of sub-wavelength objects using molybdenum of typical thickness 50 nm initially sputtered on a glass substrate is presented. A deep ultraviolet laser source at 266 nm is used. An anti-reflection layer followed by a high resolution negative tone photoresist is coated on the top of the molybdenum film. The cross-linked photoresist created after the development and bake processes is used as a mask for etching. Fabrication of the sub-wavelength object is completed using reactive ion etching in fluorinated plasma. Both 1D and 2D patterns are fabricated. The quality of the sub-wavelength objects during fabrication is checked using scanning electron microscopy, and the 1D object is characterized using TE and TM polarized illumination.

Direct writing of plasmonic nanostructures is demonstrated by nanoscale-tensile-stress induced patterning through interference crosslinking in a polymer film and by single-pulse interference ablation of a gold film. Nanoscale-tensilestress from the interference crosslinking of polymer films which are exposed to the interference pattern of UV laser beams stretches evaporated gold films and induces pattern transfer from polymer into gold nanostructures. Instead, plasmonic nanostructures can be directly patterned by the interference ablation. Being exposed to the interference pattern of an UV laser pulse, the gold is directly removed within the bright interference fringes, producing periodically arranged plasmonic nanostructures.

Plasmon resonant metal nanoparticles on substrates have been considered for use in several nanophotonic applications due to the combination of large field enhancement factors, broadband frequency control, ease of fabrication, and structural robustness that they provide. Despite the existence of a large body of work on the dependence of the nanoparticle plasmon resonance on composition and particle-substrate separation, little is known about the role of substrate roughness in these systems. This is in fact an important aspect, since particle-substrate gap sizes for which large resonance shifts are observed are of the same order of typical surface roughness of deposited films. In the present study, the plasmon resonance response of 80 nm diameter gold nanoparticles on a thermally evaporated gold film are numerically calculated based on the measured surface morphology of the gold film. By combining the measured surface data with electromagnetic simulations, it is demonstrated that the plasmon resonance wavelength of single gold nanoparticles is blueshifted on a rough gold surface compared the response on a flat gold film. The anticipated degree of spectral variation of gold nanoparticles on the rough surface is also presented. This study demonstrates that nanoscale surface roughness can become an important source of spectral variation for substrate tuned resonances that use small gap sizes.

The response of coupled metallic nanoparticles of various shapes to excitations by plane waves and an electron beam is investigated numerically within an efficient eigenvector expansion of the discrete-dipole approximation (DDA). It is shown that this procedure allows to reduce significantly the size of the system of equations to be solved (hence the computationnal effort) when one considers multiparticle systems. The results are then confronted to standard DDA for validation.

We studied physical properties of hybrid nanostructures consisting of α-NaYF₄:Tm³⁺/Yb³⁺ nanocrystals coupled to single silver nanowires. By using confocal fluorescence microscope we observed much higher intensity of the upconversion emission form nanocrystals placed in the vicinity of nanowires as compared to isolated ones. At the same time Fluorescence Life-time Imaging Microscopy demonstrates shortening of the fluorescence decays times for metal-coupled nanocrystals. We conclude that plasmon-enhanced emission rates are mainly responsible for enhanced up-conversion efficiency.

The generation of metal nanoparticles and appropriate arrays thereof in surface regions of silicate glasses was realized by means of ultraviolet laser irradiation (193 nm and 405 nm). Especially, the excimer laser irradiation of 193 nm allowed the formation of nanoscaled structures at high resolution. The precipitation of neutral metal atoms (Ag, Au) and the growth of nanostructures occur due to laser irradiation without any subsequent thermal treatments. The interesting surface plasmon resonances were registered in UV/Vis range as a function of sizes and origin of nanoparticles and of specific arrays like line grating configurations.

In artificial light harvesting systems the conversion of light into elec- trical or chemical energy happens on the femtosecond time scale, and is thought to involve the incoherent jump of an electron from the optical absorber to an electron acceptor. Here we investigate the primary dynamics of the photoinduced electronic charge transfer pro- cess in two prototypical structures: (i) a carotene-porphyrin-fullerene triad, a prototypical elementary component for an artificial light har- vesting system and (ii) a polymer:fullerene blend as a model system for an organic solar cell. Our approach [1] combines coherent femtosec- ond spectroscopy and first-principles quantum dynamics simulations. Our experimental and theoretical results provide strong evidence that the driving mechanism of the primary step within the current gener- ation cycle is a quantum-correlated wavelike motion of electrons and nuclei on a timescale of few tens of femtoseconds. We furthermore high- light the fundamental role played by the flexible interface between the light-absorbing chromophore and the charge acceptor in triggering the coherent wavelike electron-hole splitting. [1] C. A. Rozzi et al., 'Quantum coherence controls the charge separation in a prototypical arti_cial light-harvesting system', Nature Communications 4, 1603 (2013).

In this work, we fabricated and compared two complimentary plasmonic structures: the metallic circular disc array and the 2 dimensional subwavelength hole array (2DSHA). The near-field electric-field (E-field) vector distributions of the two different plasmonic structures are analyzed. We also investigated the different plasmonic structure enhancements on quantum dots infrared photodetectors (QDIP). To fully ascertain the plasmonic enhancements in QDIPs, it is crucial to understand the E-field vector distributions in the plasmonic enhanced QDIP and identify their contributions. The E-field vertical extension of different plasmonic structures and their overlap with the quantum dot (QD) active regions are also simulated. Our studies indicate that the overlapping of the E-field vectors with the QD active region is critical to improve the QDIP performance. Detailed results and analysis will be discussed in the paper. We believe that the vector field analysis not only advances the knowledge of E-field components in plasmonic structures and their interaction with the QDs, but also provides the design guidance for high performance plasmonic enhanced optoelectronic devices.

Light can exert radiation pressure on any object it encounters and that resulting optical force can be used to manipulate particles. It is natural to expect that light should push a particle forward. However, our results indicate that a lateral force can be induced in a direction perpendicular to that of the incident photon momentum if a chiral particle is placed above a substrate that does not break any left-right symmetry. Analytical theory shows that the coupling between structural chirality and the light reflected from the substrate surface induces this sideway force that pushes chiral particles with opposite handedness in opposite directions.

The complete polarimetric responses of oblique- and square- lattices of metal subwavelength hole arrays that display extraordinary optical transmission were examined. The Mueller scattering matrices were measured at normal and oblique incidence for plane wave illumination using a polarimeter employing four photoelastic modulators. The oblique array has strong natural optical activity combined with asymmetric (non-reciprocal) transmission of circularly polarized light. At oblique incidence the square lattice also shows asymmetric transmission at non-normal incidence, whenever the plane of incidence does not coincide with a mirror line. Symmetry considerations associated with non-reciprocal transmission are emphasized in a comparison with the complete polarimetric response of dissymmetric gold gammadion arrays.

Plasmonic structures produce well-known enhancement of the near-field optical intensity due to sub-wavelength optical confinement. These properties can produce a significant change of transmission and reflection upon small mechanical change of the antenna configuration. We have developed a method based on this enhanced sensitivity for cooling and amplification of a moving mirror. Using finite difference time domain method and standard optomechanical coupled-equation, different regimes of operation such as laser detuning and cavity length were studied to compare the effect of the near-field enhancement with the conventional radiation pressure. Using practical microcavity parameters, we demonstrate significantly higher cooling - or amplification- efficiency for the near-field plasmonic effect. Moreover, the volume of the system is very small. We believe that the significant efficiency improvement and reduced volume due to the proposed near-field effect can make this approach practical for many applications ranging from gravitational wave detection to photonic clocks, high precision accelerometers, atomic force microscopy, laser cooling and parametric amplification.

Manipulation of polarization states is an important feature of many applications including in telecommunication, remote sensing and photonic computing technologies. Here we present two plasmonic nanoaperture based devices for creating and filtering circularly polarized light. One acts as an ultra-compact quarter wave plate, the other, based upon a planar chiral design, leads to asymmetric transmission of left and right circularly polarized light.

In this presentation, we report direct evidence of the bosonic nature of SPPs in a scattering-based beamsplitter, in one of the most simple experiments of quantum optics - done using SPPs instead of photons propagating in air. A parametric down-conversion source is used to produce two indistinguishable photons, each of which is converted into a SPP on a metal-stripe waveguide and then made to interact through a semi-transparent Bragg mirror. In this plasmonic analog of the Hong-Ou-Mandel experiment, we measure a coincidence dip with a visibility of 72%, the signature that SPPs are bosons and that quantum interference is clearly involved.

Quantum coherence has previously been used to enhance nonlinear optical signals such as coherent Raman scattering. Near field enhancement from plasmonic nanostructures can also dramatically improve Raman signals. We investigate quantum coherence effects in plasmonic nanostructures coupled to gain media to enhance the efficiency of surface plasmon generation. We simulate the dependence of surface-enhanced coherent anti-Stokes Raman scattering (SECARS) spectra on the position and line width of the surface plasmon resonance, and attribute small (and even negative) enhancement factors to local destructive interference. We report measurements of nanoscale phase effects in SECARS of pyridazine on gold nanoparticle aggregates, and propose strategies to increase enhancement factors towards theoretical predictions.

Spontaneous emission (SE) of a Quantum emitter depends mainly on the transmission strength between the upper and lower energy levels as well as the Local Density of States (LDOS)^[1]. When a QD is placed in near a plasmon waveguide, LDOS of the QD is increased due to addition of the non-radiative decay and a plasmonic decay channel to free space emission^[2-4]. The slow velocity and dramatic concentration of the electric field of the plasmon can capture majority of the SE into guided plasmon mode (Г_pl ). This paper focused on studying the effect of waveguide height on the efficiency of coupling QD decay into plasmon mode using a numerical model based on finite elemental method (FEM). Symmetric gap waveguide considered in this paper support single mode and QD as a dipole emitter. 2D simulation models are done to find normalized Г_pl and 3D models are used to find probability of SE decaying into plasmon mode ( β) including all three decay channels. It is found out that changing gap height can increase QD-plasmon coupling, by up to a factor of 5 and optimally placed QD up to a factor of 8. To make the paper more realistic we briefly studied the effect of sharpness of the waveguide edge on SE emission into guided plasmon mode. Preliminary nano gap waveguide fabrication and testing are already underway. Authors expect to compare the theoretical results with experimental outcomes in the future.

We model a nanoparticle of organic dye molecules as an ensemble of multi-level quantum systems in order to determine the conditions necessary to yield temporal optical field enhancement for different probe energies. By utilizing a time-dependent density-matrix approach and by examination of the role played by both radiative and non-radiative decay processes between energy levels, we explore how optical pump and probe fields may be used to control the permittivity of the nanoparticle as a function of time. When an appropriate value of the permittivity occurs, a plasmon-like mode will be produced. In this work, we investigate systems in which these plasmon-like modes can be generated at probe energies detuned from the atomic transitions and sustained for timescales dependent on the lifetime of a meta-stable level in our system. Our results suggest that these plasmon-like modes may generate temporal optical field enhancement and that such nanostructures open a new realm in nanophotonics in which transient behaviour can lead to phenomena that cannot be attained in the steady-state regime.

We have proposed a metallic dipole-ellipsoid-bagel nanostructure for the generation of high harmonics via two-color laser field. Comparing with the case of the one-color field, this nanostructure enables a broader bandwidth and smoother harmonic spectra under the condition of the two-color incidence field, which is in favor of the generation of extreme-ultraviolet (XUV) radiation and isolated attosecond pulses. Numerical techniques are employed to optimize nanoantennas and attain enhanced plasmonic field. The electromagnetic properties of this nanostructure is fully analyzed and discussed. The nanostructure support the highest enhancement fact of 2500 for both of 800-nm and 1500-nm incidence, and effectively enhance the field intensity exceed 10³ in the volumn of 50×50×50 nm³.This nanostructure would benefit for the generation of high-harmonic, extreme-ultraviolet (XUV) radiation via plasmonic enhanced filed in a two-color multi-cycle laser field. This work would have potential application in the ultra-sensitive color sensor and the source of isolated attosecond pulses via multicycle laser.

Optical spectra of noble metal nano-particles supported on different types of zeolites are studied and compared. The absorbance spectra of Cu, Ag and Au nanoparticles supported on mordenite, β-zeolite, Na/Y and H/Y zeolites respectively are reported. Spectra for pre-exchanged Au-Cu/Na/Y, Au-Ni/Na/Y and Au-Fe/Na/Y are also studied. A simple effective medium approach (Maxwell-Garnett) is used to obtain a theoretical complex effective dielectric function of the composite and to asses the sensibility of the plasmon resonance to the sample characteristics. The knowledge of these properties can hopefully be applied to the development of optical tools to monitor the synthetic path.

The investigation of relaxation processes in noble metal nanoparticles upon ultrafast excitations by femtosecond laser pulses is useful to understand the origin and the enhancement mechanism of the nonlinear optical properties for metaldielectric nanocomposites. In the current work we analyze diamond like carbon (DLC) film based copper and silver nanocomposites with different metal content synthesized employing unbalanced magnetron sputtering of metal targets with argon ions in acetylene gas atmosphere. Surface morphology and nanoparticle sizes were analyzed employing scanning electron and atomic force microscopy. Optical properties of the nanocomposite films were analyzed employing UV-VIS-NIR spectrometry. Transient absorption measurements were obtained employing Yb:KGW femtosecond laser spectroscopic system (HARPIA, Light Conversion Ltd.). Energy relaxation dynamics in Cu nanoparticles showed some significant differences from Ag nanoparticles. The increase of excitation intensity hasn’t show additional nonlinear effects for the excited state relaxation dynamics for both kinds of samples.

We study the fluorescence properties of up-converting α-NaYF₄:Er³⁺/Yb³⁺ nanocrystals (NCs) in the presence of spherical Au nanoparticles. The effects of plasmon excitations in the Au nanoparticles were studied using scanning confocal fluorescence microscope. The results show that the ⁴S_3/2→ ⁴I_15/2 transition in erbium ions, which appears at 540 nm, resonant with the plasmon band of the Au nanoparticles, is efficiently quenched. In contrast, in the case of ⁴F_9/2→ ⁴I_15/2 transition, which appears at 650 nm, we find the increase of emission intensity. Complementary measurement of fluorescence lifetimes of individual NaYF₄:Er³⁺/Yb³⁺ nanocrystals reveals that plasmonic excitations in Au nanoparticles influence the dynamics of both emission band in erbium ions.

A background-suppressed surface-enhanced molecular detection technique is experimentally demonstrated by utilizing the resonant coupling of plasmonic modes of a metamaterial absorber and Infrared (IR) vibrational modes of molecules. The fabricated metamaterial consisted of one-dimensional (1D) array of Au micro-ribbons on a thick Au film separated by an MgF2 gap layer. The surface structures were designed to exhibit an anomalous IR absorption at ~ 3000 cm^-1, which spectrally overlapped with C-H stretching vibrational modes. 16-Mercaptohexadecanoic acid (16-MHDA) was used as a test molecule, which formed a 2-nm thick self-assembled monolayer (SAM) with their thiol head-group chemisorbed on the Au surface. In the FTIR measurements, the symmetric and asymmetric C-H stretching modes of the 16-MHDA were clearly observed as Fano-like anti-resonance peaks within a broad plasmonic absorption of the metamaterial. The lowbackground detection scheme with tailored plasmonic enhancement by the metamaterial absorber dramatically improved the sensitivity down to ~ 1.8 attomoles within the diffraction-limited IR beam spot. Our metamaterial approach thus may open up new avenues for realizing ultrasensitive IR inspection technologies.

Domino modes are highly-confined collectivemodes that were first predicted for a periodic arrangement of metallic parallelepipeds in far-infrared region. The main feature of domino modes is the advantageous distribution of the local electric field, which is concentrated between metallic elements (hot spots), while its penetration depth in metal is much smaller than the skin-depth. Therefore, arrays of non-resonant plasmonic nanoantennas exhibiting domino modes can be employed as broadband light trapping coatings for thin-film solar cells. However, until now in the excitation of such modes was demonstrated only in numerical simulations. Here, we for the first time demonstrate experimentally the excitation of optical domino modes in arrays of non-resonant plasmonic nanoantennas. We characterize the nanoantenna arrays produced by means of electron beam lithography both experimentally using an aperture-type near-field scanning optical microscope and numerically. The proof of domino modes concept for plasmonic arrays of nanoantennas in the visible spectral region opens new pathways for development of low-absorptive structures for effective focusing of light at the nanoscale.

We report single-photon plasmon-enhanced photoluminescence from nanostructured gold surfaces by controlling the extent of the spectral overlaps of the excitation energy hω_o, the surface plasmon resonance band (with peak resonance energy hω_SPR), and the critical points Δ_X and Δ_L, of the joint density of states of the d and sp bands, near the X- and Lsymmetry points of the electronic band structure, respectively. For hω_o~Δ_X (hω_o<Δ_X), the peak photoluminescence intensity is strongly enhanced for a strong spectral overlap of hωo~hω_SPR, and weakly enhanced for a weak spectral overlap. We show that the background continuum accompanying surface-enhanced Raman scattering (SERS) spectra from benzenethiol and 4-mercaptopyridine self-assembled monolayers chemisorbed on the nanostructured gold surfaces originates from plasmon-enhanced photoluminescence. The background continuum from silver nanostructures exhibits very different characteristics, which originates from SERS of oxide and amorphous carbon on silver surfaces.

The transmission resonances occurring in the extraordinary light transmission through metallic films with subwavelength holes can be used to tailor the spectral transmission properties of periodic slit and hole arrays. In this work we study with rigorous numerical simulations the corresponding changes in the coherence properties of electromagnetic fields transmitted through periodic subwavelength metallic gratings with narrow linear slits. Our numerical results show that by choosing suitable parameters for the grating, the degree of coherence of the beam can be significantly increased. The studied approach offers new possibilities to alter the coherence properties of fields using nanophotonic components.

Long-range surface plasmon polariton (LRSP) with lower attenuation and longer propagation length than conventional surface plasmon polariton (SPP) on a single interface has been studied as new elements for integrated optical circuits. LRSP exhibits on a metal film bounded by dielectric and can be expected to edge closer to practical use due to the long propagation length. It is theoretically predicted that the propagation length of LRSP greatly increases as the lateral width of a metal film decreases. Such mode propagating in a metal slab waveguide with extremely long propagation length is named “super LRSP”. Here, we fabricate silver slab waveguide and observe the tendency of propagation properties of super LRSP.

The practical use of graphene and graphene oxide beyond the research laboratories is strictly related to the fine tuning of new methodologies for processing and mass–production purposes. The photoreduction processing is an innovative route allowing exquisite control of the optoelectronic properties of graphene–like materials irradiated by coherent and incoherent light. We have investigated the effects induced by a mercury lamp on graphene/palladium bilayer; the change on the optical properties of the sample has been detected by using a surface plasmon resonance setup. The analysis, the perspectives and the preliminary results are shown thereafter.

Each metal presents different characteristics when used in a surface plasmon resonance (SPR) experiment. These include the shape of the SPR figure, the wavelength of better operation, the tendency to oxidize, the sensitivity to environmental changes, the range of refractive indices detectable and the capability of binding to specific targets or analytes. When choosing the metal for our SPR experiment all of these characteristics have to be taken into account. We investigate the behavior of metals, which are less or have never been used in this kind of application, comparing their characteristics to gold. We deeply investigate both theoretically and experimentally the behavior of palladium. This metal leads to an inverted curve with a maximum of reflected intensity instead of a minimum. In fact, in this case we speak of Inverted Surface Plasmon Resonance (ISPR). Aluminum and copper have also been considered because of their potentiality in specific applications.

In this work, we use the iterative Richardson-Lucy (RL) deconvolution to further increase the energy resolution of electron energy loss spectra of surface plasmon resonances (SPR) in silver nanostructures. We obtain a record e_ective energy resolution of 10 meV after 500 iterations for spectral features below 1 eV. We extract energy- _ltered maps of SPR of a nanorod at energies down to 0.25 eV, corresponding to the mid-infrared region on the electromagnetic spectrum. And we are able to identify hydrid-SPR peaks separated by only 70 meV from two nano-squares with a gap of 100 nm between them, demonstrating that the RL deconvolution applied to spectra acquired with a monochromator is a useful tool to characterize plasmonic structures at low energies with high energy resolution.

Polymer thin films embedded with plasmonic gold nanoparticles (AuNPs) are of significant interest in biomedicine, optics, photovoltaic, and nanoelectromechanical systems. Thin polydimethylsiloxane (PDMS) films containing 3-7 micron layers of AuNPs that were fabricated with a novel diffusive-reduction synthesis technique attenuated up to 85% of incoming laser light at the plasmon resonance. Rapid diffusive reduction of AuNPs into asymmetric PDMS thin films provided superior optothermal capabilities relative to thicker films in which AuNPs were reduced throughout. A photonto- heat conversion of up to 3000°C/watt was demonstrated, which represents a 3-230-fold increase over previous AuNPfunctionalized systems. Optical attenuation and thermal response increased in proportion to order of magnitude increases in tetrachloroaurate (TCA) solution concentration. Optical and thermoplasmonic responses were observed with and without an adjacent mesh support, which increased attenuation but decreased thermal response. Morphological, optical, and thermoplasmonic properties of asymmetric AuNP-PDMS films varied significantly with diffusive TCA concentration. Gold nanoparticles, networks, and conglomerates were formed via reduction as the amount of dissolved TCA increased across a log₁₀-scale. Increasing TCA concentrations caused polymer surface cratering, leading to a larger effective surface area. This method, utilizing the diffusion of TCA into a single exposed partially cured PDMS interface, could be used to replace expensive lithographic or solution synthesis of plasmon-functionalized systems.

Upconversion processes have found widespread applications in drug delivery, bio-imaging and solar-cells. In this paper we present a theoretical model that analyzes the impact of a plasmonic shield structure on the quantum yield of upconversion nanoparticles. We use this model to assess the efficiency of NaYF₄: Tm³⁺ Yb³⁺/NaYF₄ core-shell nanoparticles when embedded in a polymer matrix and covered by a metallic can-like structure. We find that as a result of this specific plasmonic structure, the upconversion luminescence from NIR to UV can be increased by a factor of 30.

Interest in the optical properties of plasmonic nanoparticles embedded in transparent polymers is expanding due to potential uses in sustainability, biomedicine, and manufacturing. Geometric optics of polydimethylsiloxane (PDMS) thin films containing uniformly or asymmetrically distributed polydisperse reduced gold nanoparticles (AuNPs) or uniformly distributed monodisperse solution synthesized AuNPs were recently evaluated using a compact linear algebraic sum. Algebraic calculation of geometric transmission, reflection, and attenuation for AuNP-PDMS films provides a simple, workable alternative to effective medium approximations, computationally expensive methods, and fitting of experimental data. Generally, transmission and reflection increased with AuNP isotropy and particle density, as displayed on a novel ternary diagram. Irregular AuNP morphology and size distribution caused optical attenuation from polydisperse films to increase in proportion to log₁₀ increases in gold content, resulting in lower attenuation per gold mass when compared to monodisperse AuNPs. Uniform monodisperse AuNP-PDMS films attenuated light in proportion to gold content, with films attenuating 0.15 fractional units per 0.1 mass-percent AuNPs. Thin layers of concentrated AuNPs attenuated light more efficiently. A 25 micron thick layer of 1.2 mass-percent AuNPs attenuated 0.5 fractional units, the same number as a 130 micron thick 0.6 mass-percent film. Measured optical responses from asymmetric AuNP-PDMS films with an adjacent back-reflector and pairs of uniformly distributed films were predictable within 0.04 units of linear algebraic estimates based on geometric optics. This approach allows for the summative optical responses of a sequence of 2D elements comprising a 3D assembly to be analyzed.

We investigate the optical conductivity and plasmon spectrum of a two-dimensional electron gas with Rashba and Dresselhaus spin-orbit interaction. Using the self-consistent field approach we derive expressions for the dispersion relations of the intra- and inter-SO plasmons. We found that the latter are immersed within the continuum of inter-SO single-particle excitations. The intra-SO plasmons remain undamped and almost unaffected by the spin-orbit coupling. Remarkably, the optical conductivity shows however a dependence on the direction of the externally applied electric field, caused by the anisotropic splitting of the spin states. In addition to the control through the driving frequency or electrical gating, this new aspect of the optical absorption spectrum might be useful in spintronics applications.

We report on the use of two-photon absorption to photocleavage o-nitrobenzyl-based ligands bound to a gold surface with thiol groups. Ablation of ligands occurs at high power densities, but this can be largely avoided by reducing the optical power level, at which point two-photon mediated reactions still occur on a time scale of tens of seconds. This means that photoactive ligands can be activated at wavelengths where plasmon resonances in gold and silver nanoparticles can easily be achieved, which will allow the surface properties at the hot spots on plasmonic nanostructures to be chosen differently from the rest of the structure, with possible applications in high-efficiency Surface-Enhanced Raman Spectroscopy and bottom-up nanoassembly.

The design, characterization, and optical modeling of aluminum nano-hole arrays are discussed for potential applications in surface plasmon resonance (SPR) sensing, surface-enhanced Raman scattering (SERS), and surface-enhanced fluorescence spectroscopy (SEFS). In addition, recently-commercialized work on narrow-band, cloaked wire grid polarizers composed of nano-stacked metal and dielectric layers patterned over 200 mm diameter wafers for projection display applications is reviewed. The stacked sub-wavelength nanowire grid results in a narrow-band reduction in reflectance by 1-2 orders of magnitude, which can be tuned throughout the visible spectrum for stray light control.

The surface plasmon (SP) excitations in the periodical array of the nanorods have attracted a lot of attention in the recent years due to the numerous potential applications in nanoplasmonics including transmitting and processing optical signals on a scale much smaller than the wavelength. In our work the plasmonic and dielectric systems consisting of twodimensional periodic arrays of nanorods are considered. We use computer simulation as well as exact analytical solution to find reflectance and transmittance the plane array of the nanorods, which have various diameters and inter-particle spacing. As the metal nanorods approach each other, series of surface plasmon resonances are excited. The resonances are strongly localized between nanorods due to its collective nature. It is shown that the local electric field is much enhanced in the interparticle gap and it concentrates at a scale much smaller than the diameter of the rod. The reflectance and transmittance have sharp minima and maxima corresponding to the excitation of various SP resonances. The computer simulations are in an agreement with our analytical theory. In the case of the dielectric nanorods the phenomenon of the whispering gallery modes effect is considered. The resonance frequencies and field enhancement can be tuned by variation of the shape and arrangement of the nanorods. The system of nanorods that almost touched each other by their generatrices can be used to develop plasmon and dielectric substrates, which are the basic elements of high sensitive SERS bio and chemical sensors.

This work reports on the theoretical and experimental research of photophysical properties of hybrid nanostructures based on gold nanoparticles (AuNp) covered by phthalocyanine (Pc) layer. We focused on the theoretical treatment of Pc molecular absorption and luminescence properties. We found out optimal sizes for the hybrid structure core when the maximum of Pc shell molecular absorption is achieved. Optimal core sizes for enhancement of the molecular luminescence were also obtained. AuNp-Pc hybrid structure with average core radius of 10 nm and Pc shell thickness of 2.5 nm were experimentally synthesized. The calculation results were compared with the experimental data, so we obtained well coincidence between each other.

Magnetic-plasmonic materials are an interesting class of materials for both fundamental and applied research. Knowledge of the optical properties and their origin in the materials is a must. Using a layer-by-layer method, we fabricated magnetic-plasmonic nanoparticle multilayers and measured their optical properties. Discrete dipole approximation calculations to model the optical properties of such materials allow us to understand the observed optical features. Comparing experimental and theoretical results provides us with a detailed insight in the build-up of the nanoparticle multilayers and shows that nanoparticles of the added layers fill holes in previous layers and improve the quality of the sample.

We propose a broadband nano-plasmonic reflector by using an asymmetric nano-ring resonator directly connected to the input and output waveguides based on metal-insulator-metal waveguides. Due to direct connection, both clockwise and counterclockwise traveling modes propagate inside the ring resonator, giving rise to resonator resonances and Mach Zehnder interference. Ultra-broad bandwidth is realized by adjusting the lengths of the ring to manipulate the resonant wavelengths and varying its widths to minimize the low-transmission ripples. An example of the plasmonic reflector with the dimensions of 200×522 nm×nm and the bandwidth of 1000 nm is numerically accomplished.

Surface plasmons have been launched from free space optical beams (at an excitation wavelength of 700 nm) and focused in the plane using concentric curved gratings (or plasmonic lenses) etched into 30 nm-thick gold films. The performance of these devices was studied with numerical simulation and verified by near-field scanning optical microscopy experiments. These plasmonic lenses have been demonstrated to focus the launched surface plasmons effectively to a high intensity focal spot.

In the last decade, several efforts have been spent in the study of near-field coupled systems, in order to induce hybridization of plasmonic modes. Within this context, particular attention has been recently paid on the possibility to couple conventional bright and dark modes. As a result of such phenomenon, a Fano resonance appears as a characteristic sharp dip in the scattering spectra. Here we show how, gradually coupling a single rod-like nanostructure to an aligned nanoantenna dimer, it is possible to induce the near-field activation of an anti-bonding dark mode. The high polarization sensitivity presented by the far-field response of T-shape trimer, combined with the sharp Fano resonance sustained by this plasmonic device, opens interesting perspectives towards a new era of photonic devices.

Rapid modeling of far-field Fano resonance supported by lattices of complex nanostructures is possible with the coupled dipole approximation (CDA) using point, dipole polarizability extrapolated from a higher order discrete dipole approximation (DDA). Fano resonance in nanostructured metamaterials has been evaluated with CDA for spheroids, for which an analytical form of particle polarizability exists. For complex structures with non-analytic polarizability, such as rings, higher order electrodynamic solutions must be employed at the cost of computation time. Point polarizability is determined from the DDA by summing individual polarizable volume elements from the modeled structure. Extraction of single nanoring polarizability from DDA permitted CDA analysis of nanoring lattices with a 40,000-fold reduction in computational time over 1000 wavelengths. Maxima and minima of predicted Fano resonance energies were within 1% of full volume elements using the DDA. This modeling technique is amenable to other complex nanostructures which exhibit primarily dipolar and/or quadrupolar resonance behavior. Rapid analysis of coupling between plasmons and photon diffraction modes in lattices of nanostructures supports design of plasmonic enhancements in sustainable energy and biomedical devices.

Plasmonic nanostructures have been shown to act as optical antennas that enhance optical devices. This study focuses on computational electromagnetic (CEM) analysis of GaAs photodetectors with gold interdigital electrodes. Experiments have shown that the photoresponse of the devices depend greatly on the electrode spacing and the polarization of the incident light. Smaller electrode spacing and transverse polarization give rise to a larger photoresponse. This computational study will simulate the optical properties of these devices to determine what plasmonic properties and optical enhancement these devices may have. The models will be solving Maxwell’s equations with a finite element method (FEM) algorithm provided by the software COMSOL Multiphysics 4.4. The preliminary results gathered from the simulations follow the same trends that were seen in the experimental data collected, that the spectral response increases when the electrode spacing decreases. Also the simulations show that incident light with the electric field polarized transversely across the electrodes produced a larger photocurrent as compared with longitudinal polarization. This dependency is similar to other plasmonic devices. The simulation results compare well with the experimental data. This work also will model enhancement effects in nanostructure devices with dimensions that are smaller than the current samples to lead the way for future nanoscale devices. By seeing the potential effects that the decreased spacing could have, it opens the door to a new set of devices on a smaller scale, potentially ones with a higher level of enhancement for these devices. In addition, the precise modeling and understanding of the effects of the parameters provides avenues to optimize the enhancement of these structures making more efficient photodetectors. Similar structures could also potentially be used for enhanced photovoltaics as well.

The nonlinear optical modulation of a light beam (or Kerr effect) by a single gold metallic nanoparticle has been obtained by the P-Scan method. The 80 nm diameter gold nanoparticles were spread on a glass substrate and investigated with a tightly focused femtosecond laser beam at the fundamental wavelength of 840 nm for different incident intensities. The retro-reflected intensity was recorded in the far field at the same wavelength of 840 nm. Clear deviations from the linear regime were observed and attributed to both nonlinear refraction and nonlinear absorption of the gold nanoparticles. Besides, the second harmonic signal was also observed for these nanoparticles allowing for the display of the linear, quadratic and cubic susceptibility tensors χ⁽¹⁾, χ⁽²⁾ and χ⁽³⁾ of the same substrate where are dispersed gold nanoparticles.