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We demonstrate spectroscopic THz reflection imaging through turbid media. We show that the detection of resonant features in the extinction spectrum can be made possible using multiresolution analysis based on wavelet transforms. We determine that the spatial resolution of this imaging technique is only diffraction limited.

Spectra of light extinction by metal nanoprisms and nanostars coated with molecular aggregates of organic dyes are calculated and theoretically analyzed. Qualitatively different nature of the spectra of organometallic nanoparticles under study is established when using J-aggregates of various cyanine dyes as their capping layer, as well as silver and gold as the cores. This results from the implementation of various plasmon-exciton coupling modes in the systems under consideration.

We calculate scattering, absorption, and extinction spectra for triangular silver nanoprisms and plasmonic nanopatch antennas (NPAs). We demonstrate that for the nanopatch antennas involving nanoprisms with a lateral size of 40–120 nm absorption prevails over scattering. Plasmon resonance for the nanoprism in water and for the NPA is redshifted relative to that for the nanoprism in air. For a single NPA plasmon resonance is redshifted with increasing the nanoprism lateral dimensions, and blue-shifted with increasing its height. We provide a guideline to optimization of the NPA design with the NPAs involving 630 nm quantum dots taken as an illustrative example.

Optical properties of a plasmonic metasurface made of a monolayer of gold nanoparticles in close proximity to an aluminum thin film were studied numerically and experimentally. Extinction spectra o...

Gold nanostars are a new type of gold nanoparticles with tunable plasmonic properties used in laser-induced biomedical applications. We investigated the effect of nanosecond pulsed laser (1064 nm) on the photomodification of gold nanostars of various sizes using TEM and spectroscopy. Photomodification of gold nanostars strongly depends on the position of their plasmonic peak in the extinction spectrum.

The optical properties of spherical, bimetallic: (core-shell) plasmonic nanostructures made of gold and silver were studied. The simulations were performed using the boundary element method. The refractive index sensitivity (RIS) of the nanoparticles was calculated from the peak shift in the extinction spectrum due to the change of the surrounding medium's refractive index. The effect of the particle's material, the size of the core, and the shell on the extinction spectrum and the RIS were investigated and they were compared with the data of the pure spherical nanoparticles.

In this work, the all plasmonic bands of supershape nanoparticle dimers were investigated using finite difference time domain simulations. The localized surface plasmons of dimers were extracted from extinction spectra. The effects of different surrounding materials and dimer gaps were reported on dimer plasmons. The obtained results showed that there exist the multiple plasmonic modes in supershape nanoparticle dimers. The electric field distribution of supershape nanoparticle dimers was studied at resonance wavelength of dimer plasmons. We found that formation bonding modes in dimers can be related to creation hot spots in low dimer gap. This study can be a base for the characterization of multiple dimer plasmons in plasmonic devices for sensing applications.

We simulated the extinction spectra of Ag–Au alloyed nanoparticles produced by pulsed laser ablation in liquid of elemental targets followed by re-irradiation of suitable mixtures of the obtained c...

The process of fragmentation of gold nanoparticles in water exposed to nanosecond IR laser radiation (1060 – 1070 nm) is studied. The behaviour of the size distribution and extinction spectrum of nanoparticles is investigated at different experimental parameters. The dependences of the size distribution maximum position and distribution width on the laser pulse duration and the corresponding characteristics of the laser plasma, arising on the nanoparticles, are analysed. The results are explained by the plasma influence on the laser radiation absorption by the colloidal solution.

The systems design aspects of surface plasmon resonance sensors, including the usually employed interrogation modes (AIM, WIM and IM) and the localized surface plasmon resonance (LSPR) are also discussed in this chapter.

The two-dimensionality of graphene and other layered materials can be exploited to simplify the theoretical description of their plasmonic and polaritonic modes. We present an analytical theory that allows us to simulate these excitations in laterally patterned structures in terms of plasmon wave functions (PWFs). Closed-form expressions are offered for their associated extinction spectra, involving only two real parameters for each plasmon mode and graphene morphology, which we calculate and tabulate once and for all. Classical and quantum-mechanical formulations of this PWF formalism are introduced, in excellent mutual agreement for armchaired islands with >10 nm characteristic size. Examples of application are presented to predict both plasmon-induced transparency in interacting nanoribbons and excellent sensing capabilities through the response to the dielectric environment. We argue that the PWF formalism has general applicability and allows us to analytically describe a wide range of 2D polaritonic behavior, thus providing a convenient tool for the design of actual devices.

Gold nanorings have special optical properties, the surface of which show an obvious Localized Surface Plasmon Resonance (LSPR) phenomena with two extinction peaks. The Discrete Dipole Approximation (DDA) method is to simulate the extinction spectrum of gold nanorings with different sizes. Simulation results revealed that plasmon wavelength changed with the size of nanorings and ambient medium. Refractive index (RI) sensitivities of gold nanorings with different sizes were calculated and gold nanorings exhibited a higher RI sensitivity than other shape, which had a broad application in biosensors.

A simple theoretical model was developed to analyze the extinction spectrum of gold nanoparticles (AuNPs) on the fiber core and glass surfaces in order to aid the determination of the surface coverage and surface distribution of the AuNPs on the fiber core surface for sensitivity optimization of the fiber optic particle plasmon resonance (FOPPR) sensor. The extinction spectrum of AuNPs comprises of the interband absorption of AuNPs, non-interacting plasmon resonance (PR) band due to isolated AuNPs, and coupled PR band of interacting AuNPs. When the surface coverage is smaller than 12.2%, the plasmon coupling effect can almost be ignored. This method is also applied to understand the refractive index sensitivity of the FOPPR sensor with respect to the non-interacting PR band and the coupled PR band. In terms of wavelength sensitivity at a surface coverage of 18.6%, the refractive index sensitivity of the coupled PR band (205.5 nm/RIU) is greater than that of the non-interacting PR band (349.1 nm/RIU). In terms of extinction sensitivity, refractive index sensitivity of the coupled PR band (&minus, 3.86/RIU) is similar to that of the non-interacting PR band (&minus, 3.93/RIU). Both maximum wavelength and extinction sensitivities were found at a surface coverage of 15.2%.

Metal nanoarchitectures producing optical responses in the visible and near-infrared form the foundation for most plasmonic studies. In contrast, a relative lack of infrared-active substrates has limited the exploration of plasmonic behavior beyond the near-infrared. In this study, we investigate the polarization-dependent, multimodal localized plasmon resonances of asymmetric nanocrescents for large diameter structures composed of gold and silver. The extended size (0.5–3.0 μm) shifts the plasmon resonances into the mid-infrared (mid-IR) spectral range. Polarization-dependent localized surface plasmon resonance (LSPR) behavior is maintained for nanocrescent diameters up to several microns due to the preservation of nanoscale structural features that result in high aspect ratios. Simulations of the extinction spectra and near-field distributions support experimentally observed plasmonic behavior. Manipulation of nanocrescent plasmon resonances in the mid-IR spectral range through structural-based tuning a...

We have simulated the extinction spectra of Au triangular nanoprisms and nanoboxes by finite difference time domain method. It is found that the refractive index sensitivity increases linearly and near exponentially as the aspect ratio of nanoprisms increases and wall thickness of nanoboxes decreases, respectively. A sensing figure of merit (FOM) calculation shows that there is an optimum wall thickness for each edge length and height of the box, which makes them to be promising candidates for effective sensing applications. We have also shown that the higher FOM in triangular nanoboxes compared to the cubic nanoboxes and other solid structure is inherent in the shape of nanoparticles.

This paper reports on physical principles and the relations between extinction cross section and geometrical properties of silver and gold nanostructures. We introduce some simple relations for determining geometrical properties of silver and gold nanospheres based on the situation of their plasmonic peak. We also applied, investigated and compared the accuracy of these relations using other published works in order to make clear the effects of shape, size distribution and refractive index of particles’ embedding medium. Finally, we extended the equations to non-spherical particles and investigated their accuracy. We found that modified forms of the equations may lead to more exact results for non-spherical metal particles, but for better results, modified equations should depend on shape and size distribution of particles. It seems that these equations are not applicable to particles with corners sharper than cubes' corners i.e. nanostructures with spatial angles less than π/2 sr.

Electrically pumped random lasing has been realized in Au/MgO/ZnO structures. By incorporating Ag nanoparticles, whose extinction spectrum overlaps well with the emission spectrum of the structures, the threshold of the random lasing can be decreased from 63 mA to 21 mA. The decrease in the threshold has been attributed to the resonant coupling between the carriers in the active layer of the structures and the surface plasmon of the Ag nanoparticles.

In this study, we observe that a dark mode is not necessarily prerequisite for an asymmetric Fano resonance to take place in plasmonic structures. The characteristic asymmetry feature of Fano resonance is retained in a plasmonic structure when both superradiant and subradiant oscillators are externally driven. Double Fano resonances are experimentally and theoretically observed where a common subradiant driven oscillator is coupled with two superradiant oscillators. As a classical analogue of a four-level tripod atomic system, the extinction spectrum of the composite metamaterial exhibits a coherent effect based on double Fano resonances. Transfer of the absorbed power between two orthogonal superradiant oscillators is shown to be mediated by the common subradiant oscillator.

The Discrete Dipole Approximation (DDA) method and the Finite Difference Time Domain (FDTD) method are used to analyze silver nanospheres with different radius and the coupling of nanospheres array complementarily. DDA method is used for simulating the extinction spectra of single silver nanosphere and nanospheres array; and the coupling of two nanospheres and their surrounding electric field distribution are simulated by FDTD method. Through these results, we got some important conclusions of nanoparticles’ Localized Surface Plasmon Resonance (LSPR) phenomenon.

We present a combination of experiments and theoretical simulations to investigate the optical response of Au/Ag alloyed hollow nanoshells. The results show that two distinct plasmon resonances corresponding to the dipolar and quadrupolar modes appear in the extinction spectra of nanoshells. As the thickness of the shell decreases the multiple modes consistently red shift and the resonant intensity increases. The results are validated by the calculated electric field distribution of nanoshells.

The effect of defects such as vacancies, dislocations, and interstices on the extinction spectra of colloidal crystals consisting of plasmon resonance silver nanoparticles is investigated. The possibility of using extinction spectra for the express monitoring of individual and combined defects is discussed.

The extinction spectra and electric field distributions of hollow triangular nanoprisms are calculated using the discrete dipole approximation method and compared with those of the solid triangular nanoprisms. When light propagates along the prisms, the main plasmon peaks of hollow triangular nanoprisms red shift compared with those of the solid triangular nanoprisms. At the main plasmon peaks, the hollow triangular nanoprisms provide more hot spots than the solid triangular nanoprisms. Therefore, the hollow triangular nanoprisms are more surface-enhanced Raman scattering active than the solid triangular prisms and can be used to detect small amount of molecules. For the hollow triangular nanoprism, although the local electric field distribution extremely relates to the incident polarization, the extinction spectra are independent of the incident polarization. In addition, the main plasmon peaks red shift linearly with the edge length, while they blue shift exponentially with the increase of the thickness of the hollow triangular nanoprisms. These results could be used to engineer hollow triangular nanoprisms for specific plasmonic applications.

We have developed an efficient parameterization of the dielectric properties of Au and Ag in the energy range between 0.6 eV and 6.6 eV. The resulting time-domain dielectric function can be used for finite-difference time-domain (FDTD) simulations of the optical properties of nanoparticles. We present FDTD calculations of the extinction spectra of various Au and Ag nanoparticles and show that the calculated spectra agree very well with exact calculations using experimentally measured dielectric functions.

We discuss some optical properties of cellulose nanocrystals decorated with silver nanospheres. We give a short description of the discrete dipole interactions, and the broadening effects observed in the extinction spectrum. We also discuss some preliminary results for their use in organic photovoltaic devices.

We present a strategy for enhancing the photoluminescence intensity of semiconductor quantum dots (QDs) by plasmonic light concentration by nanodiscs. The enhancement can be tuned by tailoring the extinction spectrum of the nanostructures for the QD emission wavelengths.

We study the influence of positional disorder on the optical properties of metallic photonic crystals. Two disorder models are implemented, namely frozen-phonon disorder and long-range disorder. We calculate the two-point correlation functions, analyze the Fourier transforms of the spatial arrangements, and present experimental extinction spectra of the different disordered photonic crystals.

We present an observation of depolarized scattering by silver colloids. The profile of the wavelength-dependent anisotropy of the colloidal solution of silver nanoparticles traces the plasmonic extinction spectrum. The scattering component of the colloid extinction spectrum is responsible for the depolarization effect. We believe that the presence of the orthogonal component in the silver colloid scattering can be used in dye-less sensing devices.

The dispersion curves of the surface electrostatic and magnetostatic modes of a spherical shell which is made of a material with dispersive permittivity and permeability, and which has a negative refractive index over a frequency band, are calculated. Both the case of a dielectric core and that of a metallic core are treated. The extinction properties of the shell are derived, and the dependence of the extinction spectrum on the geometrical parameters is investigated.

The optical response of a two-dimensional periodic array of metallic nanoparticles on a dielectric waveguide is investigated by means of numerical calculations using the on-shell layer-multiple-scattering method. We find that the strong interaction between particle-plasmon and waveguide modes influences drastically the extinction spectrum of the system. Our results explain successfully available experimental data and provide a transparent physical picture of the underlying processes.

The dispersion curves of the surface polaritons of a cylinder which is made of a material with dispersive permittivity and permeability, and which is left-handed over a frequency band, are calculated. It is found that there exist three surface mode bands. With increasing wavevector the three bands converge to three limiting frequencies, which are equal to the three corresponding frequencies obtained for the slab geometry. The extinction properties of the cylinder are derived, and the dependence of the extinction spectrum on the cylinder radius is investigated.

Extinction spectra of spheres made of materials having dispersive permittivity and permeability are calculated. A dispersion in the microwave region, similar to that which has recently been achieved in artificial composite media is assumed. When either the permittivity or the permeability (but not both) is negative, there occurs a band of strong surface polariton absorption. However, when both quantities are negative, a band of highly suppressed extinction appears in the spectrum.

The plasmonic properties of two closely adjacent gold nanocones of different sizes have been investigated. The plasmon modes of the first nanocone couple with the plasmon modes of the second one due to which a broad peak and a narrow peak emerges in the extinction spectrum, which can be categorized as bright and dark plasmon modes. The destructive interference of the two modes results in a sharp Fano dip in the spectrum. Several configurations of the conical nanodimer have been considered, which suggests that the plasmon coupling in the nanocone dimer is not only dependent on the interparticle distance and size of the nanoparticles but also on their spatial arrangement. The localized high near-field energy in the nanodimer can be used for surface-enhanced Raman spectroscopy applications.

The optical properties of nanostructured architectures are highly sensitive to their compositions, structures, dimensions, geometries and embedding mediums. Nanopolyhedra, including homogeneous metal nanoparticles and core-shell structures, have unique optical properties. In the beginning of this study, Discrete Dipole Approximation (DDA) method has been introduced. Then the simulated extinction spectra of single-component metal nanoparticles and Au@Ag polyhedra were calculated using both Mie and DDA methods. The influence of morphology and components on the optical response is discussed and well-supported by previously published experimental results. It is observed that the Localized Surface Plasmon Resonance peaks are mainly decided by sharp vertexes and symmetry of noble metallic polyhedra, as well as the structure of the Au@Ag core-shell nanoparticles.

Plasmonics is the title given to the optical phenomenon related to plasma oscillations in metals.

Noble metal nanoparticles exhibit fascinating geometrically tunable optical properties that are dominated by their localized surface plasmon resonances (LSPRs). By judiciously tailoring the geometric parameters of a metal nanoparticle, one can fine-tune the nanoparticle’s optical responses in a precisely controllable manner and thereby selectively implement desired optical properties into nanomaterial systems or nanodevices for specific applications. In this chapter, we present a review on the recent experimental and theoretical advances in the understanding of the geometry–optical property relationship of metallic nanoparticles in various geometries.

Light scattering by arrays of metal nanoparticles gives rise to nanostructured optical fields exhibiting strong and spatially localized (on a nanometer scale) field intensity enhancements that play a major role in various surface phenomena.

Optimization of metallic nanoparticles was presented in this paper by aid of computational numerical calculation. The optical extinction spectra of rhombic hybrid Au-Ag nanoparticles have been calculated by the discrete dipole approximation (DDA) aided design method. Both material and the thickness of the particles can be used to effectively tune localized surface plasmon resonance. On the basis of the calculated extinction spectra, the crucial parameters of the nanostructure arrays such as thickness can be determined. Using this DDA aided approach, a hybrid Au-Ag nanoparticles array is put forth and designed with the optimized parameter of thickness of metal thin films (h(Au) = 5 nm, and h(Ag) = 25 nm). This study shows that the material of the particles have significant effect on the optical properties. The DDA aided design method can provide the optimized structure parameters for the hybrid nanostructures.

Metal nanoparticles have become increasingly important in fields such as electronics, photonics, and biotechnology. In particular, anisotropic gold nanoparticles, such as gold nanorods, exhibit unique properties owing to their anisotropy. Optical properties of isolated gold nanorods and dimers of gold nanorods have been investigated from both experimental and theoretical points of view. We have reported a method for three-dimensional assembly of anisotropic gold nanoparticles by two-phase transfer in which the morphologies of the assemblies can be controlled by the aspect ratio of nanorods. In this study, we numerically calculate extinction spectra to investigate the plasmonic properties of bundlelike assemblies by the finite-element method. Their plasmonic properties depend on not only the three orthogonal directions but also the alignment of the nanorod assembly.

The time-dependence evolution of the extinction spectra of the silver nanoplates is studied to analyze the underlying physical mechanism of the growth process. As the synthesis cycles increase, the wavelength of the absorption peak is first blue-shifted and then is followed by the red shift, attributing to the mode alteration of the longitudinal surface plasmon resonance of the silver nanoplates. The capping agents are also optimized for the convenient and speedy growth of the large integrated Ag nanostructure. These observations expand the comprehensive understanding of plasmon resonance of the Ag nanoplates, and give a better manipulation of their applications in the plasmonic nanodevices.

Extended branched networks of single-nanoparticle chains have recently been self-assembled from colloidal suspensions. In particular, gold nanoparticle linear chains and complex chain networks have revealed unique signatures of plasmon modes in their extinction spectra. In this Letter, we investigate theoretically their near-field optical properties and show that a real space mapping of these modes can be achieved with a photon scanning tunneling microscope setup. A distinct subwavelength patterning of the optical near-field gives rise to well-resolved photon scanning tunneling microscope images that can be used to identify the network segments able to efficiently carry optical energy.

As optical trapping by a focused laser beam is applied for nanoparticles, multiple particles are grasped in the focal spot and make an assembly. Gold nanoparticles confined in such a submicrometer optical cage show a characteristic extinction spectrum depending on laser power. The spectral change can be induced reversibly and repeatedly by tuning the laser power, demonstrating that the assembly of gold nanoparticles can be controlled by the gradient force. This is attributed to the soft confinement of nanoparticles dressed in electrostatic potential barriers.

Cataloged from PDF version of article. We fabricated localized surface plasmon resonance enhanced UV photodetectors on MOCVD grown semi-insulating GaN. Plasmonic resonance in the UV region was attained using 36nm diameter Al nanoparticles. Extinction spectra of the nanoparticles were measured through spectral transmission measurements. A resonant extinction peak around 300nm was obtained with Al nanoparticles. These particles gave rise to enhanced absorption in GaN at 340nm. Spectral responsivity measurements revealed an enhancement factor of 1.5. These results provided experimental verification for obtaining field enhancement by using Al nanoparticles on GaN. © 2012 IOP Publishing Ltd.

In this paper, localized surface plasmon enhanced n-ZnO/i-ZnO/MgO/p-GaN structured light-emitting devices have been designed and constructed. It is found that the electroluminescence of the devices can be enhanced at selective wavelengths that match the localized surface plasmon extinction spectra of the metal nanoparticles.

The effects of various parameters including thickness and dielectric constants of substrates, shapes of nanoparticles, and polarization direction of incident light, on the extinction spectra of periodic gold nanoparticle arrays are investigated by the full-vectorial three-dimensional (3D) finite difference time domain (FDTD) method. The calculated results show that the substrate affects the extinction spectra by coupling the fields co-excited by the substrate and gold nanoparticles. Extinction spectra are influenced by the shapes of the nanoparticles, but there are no obvious changes in extinction spectra for similar shapes. The polarization direction of incident light has a great influence on the extinction spectra. The implications of these results are discussed.

The extinction spectra and field distribution of Ag helical nanostructures have been calculated using the discrete dipole approximation method. The plasmon peak of the Ag helix can be tuned not only by the structural parameters but also by the polarizations of the incident light, especially the circular polarizations. In addition, the polarization direction of the incident light can change the spatial distribution of the maximum E field, which provides a simple way to spatially resolve analyte’s distribution on the nanostructures for sensing applications.

The optical extinction spectra of four topologically different Ag nanorod structures, needle, periodic, L, and Y shapes, have been calculated by the discrete dipole approximation. Both the needle and periodic shaped nanorods can be used to effectively tune plasmon resonant peaks, while the L- and Y-shaped nanorods influence the shape of the extinction spectra. This study shows that the topologic defects of nanorods have significant effects on the optical properties, and provides an alternative way to tune the plasmonic characteristics of metallic nanorods.

The two-dimensionality of graphene and other layered materials can be exploited to simplify the theoretical description of their plasmonic and polaritonic modes. We present an analytical theory that allows us to simulate these excitations in terms of plasmon wave functions (PWFs). Closed-form expressions are offered for their associated extinction spectra, involving only two real parameters for each plasmon mode and graphene morphology, which we calculate and tabulate once and for all. Classical and quantum-mechanical formulations of this PWF formalism are introduced, in excellent mutual agreement for armchaired islands with $>10\,$nm characteristic size. Examples of application are presented to predict both plasmon-induced transparency in interacting nanoribbons and excellent sensing capabilities through the response to the dielectric environment. We argue that the PWF formalism has general applicability and allows us to analytically describe a wide range of 2D polaritonic behavior, thus facilitating their use for the design of actual devices.