Femtosecond laser induced nonthermal processing is an emerging nanofabrication technique for delicate plasmonic devices. In this work we present a detailed investigation on the interaction between ultra-short pulses and silver nanomaterials, both experimentally and theoretically. We systematically study the laser-silver interaction at a laser fluent from 1 J/m² to 1 MJ/m². The optimal processing window for welding of silver nanowires occurs at fluences of 200-450 J/m². The femtosecond laser-induced surface melting allows precise welding of silver nanowires for "T” and “X” shape circuits. These welded plasmonic circuits are successfully applied for routining light propagation.

Plasmonic modes with long radiative lifetimes combine strong nanoscale light confinement with a narrow spectral line width carrying the signature of Fano resonances. The interplay between radiative and non-radiative lifetimes of subradiant modes critically determines their optical properties and optimal use in nanoplasmonic applications. Here, it is shown analytically and numerically with the example of a silver nanostructure that the coupling to radiation of a subradiant mode, its radiance, can be classified into three different regimes. The modulation damping is a unitless lineshape parameter which provides direct information on the radiance. In the weak coupling regime, subradiant modes are very sensitive to geometrical displacements and deformations. Strong modulation of their spectral lineshape is also observed. At critical coupling, the radiative and non-radiative decays are balanced and the electromagnetic energy stored in the mode is maximal. For larger coupling, hybridization of the modes may be observed. In general, the classification of the coupling regimes presented here provides a systematic way to choose the most adapted coupling regime for specific nanoplasmonic applications.

In this paper, the effect of tapered asymmetrical gammadion on the optical rotational properties and sensitivity detection of biomolecular structures is presented. The asymmetrical structure is made up of gold material on a glass structure and immersed in water. The chirality of the un-rotated array is first determined by measuring the circular dichroism (CD) spectrum. Three modes, arising from Bloch periodic theory and surface resonance mode are observed. Then each asymmetrical gammadion structure is tapered at the arms. Tapering fraction, which define the ratio of tapered end to the untapered end is used for defining the new design. The designs are then fabricated using e-beam lithography and tested using the polarimeter for CD spectra. The spectra show that the three CD modes changes in degree amplitude and wavelength, especially for smaller tapering fractions.

Extraordinary optical transmission (EOT) through highly conductive ZnO films with sub-wavelength hole arrays is investigated in the long-wavelength infrared regime. EOT is facilitated by the excitation of surface plasmon polaritons (SPPs) and can be tuned utilizing the physical structure size such as period. Pulse laser deposited Ga-doped ZnO has been shown to have fluctuations in optical and electrical parameters based on fabrication techniques, providing a complimentary tuning means. The sub-wavelength 2D hole arrays are fabricated in the Ga-doped ZnO films via standard lithography and etching processes. Optical reflection measurements completed with a microscope coupled FTIR system contain absorption resonances that are in agreement with analytical theories for excitation of SPPs on 2D structures. EOT through Ga-doped ZnO is numerically demonstrated at wavelengths where SPPs are excited. This highly conductive ZnO EOT structure may prove useful in novel integrated components such as tunable biosensors or surface plasmon coupling mechanisms.

In this work, a trilayer graphene is used as a thin non dielectric spacer with a high index of refraction, between Au film and Au NPs. Encouraged by the sharpness of the localized surface plasmon resonance LSPR induced by this system, we performed sensitivity measurements to refractive index change in the surrounding medium of the sensor. The presence of graphene led to both higher sensitivity and sharper full width at half maximum FWHM and thus higher figure of merit FOM (2.8) compared to the system without graphene (2.1).

We theoretically investigate the propagation of graphene plasmon polaritons in graphene nanoribbon waveguides and experimentally observe the excitation of the graphene plasmon polaritons in a continuous graphene monolayer. We show that graphene nanoribbon bends do not induce any additional loss and nanofocusing occurs in a tapered graphene nanoriboon, and we experimentally demonstrate the excitation of graphene plasmon polaritonss in a continuous graphene monolayer assisted by a two-dimensional subwavelength silicon grating.

We present an innovative method for modulating light using a ferroelectric thin-film embedded with metal nanoparticles. Due to the electro-optic effect in ferroelectric PZT, changes in refractive index can be controlled by an external electric field. Consequently, the local surface plasmon resonance of embedded noble metal nanoparticles changes with the media's refractive index. As a result, their optical extinction cross-section is shifted and light passing through the film could be controlled. In other words, an external electric field could modulate light. Using Mie theory for spherical particles, we were able to approximate the metallic nanoparticle's diameter that generates the maximum optical contrast, at a given wavelength. In addition, to establish an accurate model, we considered the impact on plasmon resonance resulting from deformation of the nanoparticles. The deformation is caused by the piezoelectric property of the ferroelectric host material. We assumed 20 nm diameter Au or Ag nanoparticles embedded in a 1 μm thick PZT film. Simulations showed that these particles can reach an optical contrast of up to 12 dB, in the visible spectrum. In addition, deformation of particles had negligible impact on the shift in resonance frequency compared to the change in PZT refractive index. In this study we have shown that a nanocomposite comprising of nanoparticles embedded PZT thin film can perform as an optical modulator. This modulator will be able to achieve a high contrast with low power consumption.

It has recently been experimentally demonstrated that reproducible and controllable all-optical magnetization reversal in GdFeCo films can be achieved with a single ultrafast (from 40fs to 3ps) femtosecond laser pulse. While the microscopic origin of the effect is still unclear, we suggest that the effect is caused by a combination of light-induced quasi-static magnetic field, with dynamic thermal effects due to laser heating, as well as magnetic fields generated by thermoelectric effect-caused electrical currents. This finding reveals great potential for ultrafast data storage through magnetic switching without the aid of an external magnetic field. It was further recently predicted that utilization of plasmonic nanostructures may provide the way to achieve fast all-optical magnetization switching with smaller/cheaper laser sources with longer pulse durations. We will present the simulations of temporal dynamics of magnetization reversal around plasmonic nanostructures with the combination of Landau Lifshitz Bloch and finite element modeling. Our modeling results predict that plasmonic nanostructures can significantly alter all-optical magnetization switching process and may help achieve a number of technologically important effects that cannot be achieved otherwise. Results of experimental studies of optical magnetization reversal in GdFeCo films around plasmonic nanostructures are also provided.

Using the quasistatic approximation, we calculate the dispersion relations for plasmonic waves along a chain of metallic nanoparticles when the host is a nematic or a cholesteric liquid crystal (NLC or CLC). If the director of the NLC is perpendicular to the chain, the doubly degenerate transverse (T) branches split into two linearly polarized branches. For a CLC with a twist axis parallel to the chain, the two T branches again split, but are no longer linearly polarized. We illustrate these results numerically by calculating the dispersion relations for Drude metal particles in either an NLC or a CLC.

We study cooperative effects in energy transfer from an ensemble of donors to an acceptor near a plasmonic nanostructure. We demonstrate that plasmonic coupling between donors changes the energy content of the system and hence dramatically affects transfer of its energy to an outside acceptor. When donors are situated in a close proximity to the metal surface, the transfer is strongly reduced relative to one from independent donors due to additional dissipation caused by plasmon exchange between individual donors. With increasing donors’ separation from the metal, dissipation becomes less prevalent and the system transitions to cooperative regime described by plasmonic superradiant and subradiant eigenstates. We find that energy transfer from either one is significantly (~10) more efficient than from independent donors due to much stronger coupling of superradiant states to the acceptor and much weaker damping of subradiant states. We develop a theory for cooperative plasmon-enhanced energy transfer and present numerical results demonstrating the amplification effect for a layer of donors and an acceptor on spherical plasmonic nanoparticle.

Second harmonic generation microscopy is used for the investigation of the nonlinear optical response of single gold nanowires and aggregates of quasi-spherical gold nanomaterials. Angular and spectral resolved approaches are performed to study the origin of the second harmonic emission (SH) from isolated gold nanowire, nanosphere and interacting nanospheres in aggregates. It is observed that the Second harmonic efficiency is enhanced when the excitation wavelength is resonant with the surface plasmon mode (SP) of the metallic nanomaterials. The angular resolved second harmonic analysis study demonstrated the presence of different origins (dipolar, quadrupolar and octupolar modes) involved in the nonlinear optical emission from gold nanowires and nanospheres. Our investigation demonstrates the important role of electric dipole arising from the breaking of the centrosymmetry at the surface of the nanowire and imperfect spherical shape of the gold nanospheres, and in the size regime below 50 nm. The increase of the aggregate and nanowire size induces the presence of interferences between higher orders (quadrupole) and dipole sources. For size higher than 50 nm, the analysis of the angular resolved emission pattern demonstrates the presence of retardation effects and the deviation from the dipolar emission picture. The results are in good agreement with the actual reported results in terms of character of emission. Finally, the SH emission of gold nanowire was spectrally analyzed for single gold nanowire and variable aggregates size. A clear SH emission is observed at 2ω for each excitation frequency ω with the presence of 2 photons visible photoluminescence emission (2PL).

Coupling between electronic state and far field light, including absorption and spontaneous emission, is a central issue for applications such as quantum metrology, optical quantum information, single molecule fluorescence spectroscopy, and ultra sensitive detection which demand on high quantum efficiency. In such applications, propagating far field light with diffraction limited spatial distribution has to be coupled to the electronic state of a quantum absorber/emitter with a size far below the diffraction limit. Such a significant contrast between the wavelengths of photon and electron sets limitations on the light-matter interaction strength. The most straight forward solution is to convert far-field modes to near-field modes with dimensional scale closer to the electronic state. The process of converting far field to near field and vice versa can be conducted by an antenna as an intermediate element between far field mode and electronic state in a quantum element (absorber/emitter). Here, we classify optical antenna based on their performance into three categories. Considering each category advantage, we propose a hybrid antenna with superior performance. A quantum efficiency of about 50% is predicted for a semiconductor with volume of ~λ3/170. Despite the weak optical absorption coefficient of 2000 cm^-1 in the long infrared wavelength of ~8 μm, very strong far-filed coupling has been achieved, as evidenced by an axial directivity gain of 16 dB, which is only 3 dB bellow of theoretical limit.

The loss in optical antennas can affect their performance for their practical use in many branches of science such as biological and solar cell applications. However the big question is that how much loss is due to the joule heating in the metals. This would affect the efficiency of solar cells and is very important for single photon detection and also for some applications where high heat generation in nanoantennas is desirable, for example, payload release for cancer treatment. There are few groups who have done temperature measurements by methods such as Raman spectroscopy or fluorescence polarization anisotropy. The latter method, which is more reliable than Raman spectroscopy, requires the deposition of fluorescent molecules on the antenna surface. The molecules and the polarization of radiation rotate depending upon the surface temperature. The reported temperature measurement accuracy in this method is about 0.1° C. Here we present a method based on thermo-reflectance that allows better temperature accuracy as well as spatial resolution of 500 nm. Moreover, this method does not require the addition of new materials to the nanoantenna. We present the measured heat dissipation from bull’s-eye nanoantennas and compare them with 3D simulation results.

We have been studied a finite asymmetric metal-insulator-metal (MIM) structure on glass plate for near-future visible light communication (VLC) system with white LED illuminations in the living space (DOI: 10.1117/12.929201). The metal layers are vacuum-evaporated thin silver (Ag) films (around 50 nm and 200 nm, respectively), and the insulator layer (around 150 nm) is composed of magnesium fluoride (MgF2). A characteristic narrow band filtering of the MIM structure at visible region might cause a confinement of intense surface plasmon polaritons (SPPs) at specific monochromatic frequency inside a subwavelength insulator layer of the MIM structure. Central wavelength and depth of such absorption dip in flat spectral reflectance curve is controlled by changing thicknesses of both insulator and thinner metal layers. On the other hand, we have proposed a twin-hole pass-through wave guide for SPPs in thick Ag film (DOI: 10.1117/12.863587). At that time, the twin-hole converted a incoming plane light wave into a pair of channel plasmon polaritons (CPPs), and united them at rear surface of the Ag film. This research is having an eye to extract, guide, and focus the SPPs through a thicker metal layer of the MIM with FIBed subwavelength pass-through holes. The expected outcome is a creation of noble, monochromatic, and tunable fiber probe for scanning near-field optical microscopes (SNOMs) with intense white light sources. Basic experimental and FEM simulation results will be presented.

Nanostructured electrodes and interfaces can enhance light absorption in organic solar cells due to efficient light harvesting. Ultrathin films of an active layer (C60) deposited on nanostructured grating electrodes show more absorption as a result of increased light trapping. Plasmonic nanostructured electrodes with various geometries and dimensions have been fabricated on printed polyacrylonitrile (PAN) and subsequently characterized. Surface enhanced Raman scattering (SERS) measurements show significant signal enhancement (over two orders of magnitude) on nanostructured samples when compared to planar Ag substrates due to local electromagnetic field enhancement. Furthermore, conversion of PAN to graphitic carbon is evidenced in SERS spectra. The surface area was determined using underpotential deposition (UPD) of thallium and agrees with the geometric surface area calculated from SEM images. The FDTD simulated electric field distribution inside the samples confirms the experimental results. A 60 fold increase in the electric field results in three to four orders of magnitude enhancement in the SERS signal depending on the dimensions of the pillars and gratings. Further study of the interaction between a top organic layer (C60) and the Ag electrode will help us to understand the nanoscale charge transfer rate critical to optimization and design of efficient organic solar cells.

Optical field enhancement in coupled plasmonic nanostructures has attracted significant attention because of field enhancement factors that significantly exceed those observed in isolated nanostructures. While previous studies demonstrated the existence of such cascaded field enhancement in coupled nanospheres with identical composition, this effect has not yet been studied in systems containing multiple materials. Here, we investigate the polarization-dependent optical response of multi-material trimer nanostructures composed of Au nanoparticles surrounded by two Ag nanoparticles as a function of nanoparticle size and inter-particle spacing. We observe field enhancement factors that are ten times larger than observed in isolated Au nanoparticles.

Periodic arrays of sub-wavelength structures have garnered significant interest for surface enhanced Raman spectroscopy (SERS) and metal enhanced fluorescence (MEF), and for anti-reflective coating properties. For SERS and MEF, coupling metal nanoparticles with nanometer scale spacing can induce strong local electromagnetic field enhancements at the plasmon resonance, significantly increasing the Raman signal or fluorescence of a molecule. Inspired by moth eyes, metal nanoparticle arrays can reduce the reflection of incident light, shown useful for improving the efficiency of solar cells. Here, we present fabrication of robust, tunable, inexpensive and quickly reproducible gold coated, nanopillar arrays for applications in enhancing Raman/fluorescence signals or antireflective surfaces for efficient solar cells. To create homogenous metallic nanostructures with controllable sizes and interparticle spacings, we have integrated conventional nanosphere lithography techniques with thermally responsive polyolefin (PO) films. Spin coating 500 nm PS beads onto PO substrates, followed by oxygen plasma etching, is used to vary the size and periodicity of the resulting PS nanopillar bead array. A 50 nm thick gold film can then be added using chemical vapor deposition (CVD). Nanostructures were characterized with scanning electron microscopy and atomic force microscopy. When heated from room temperature up to 115oC, structures on PO films undergo a reduction in feature size and interparticle spacing by up to 35 % in length and 50% in surface area.

Chemical sensing applications utilizing surface enhanced Raman spectroscopy (SERS) have drawn significant attention recently. However, developing a reliable, high performance SERS platform remains a challenge. A novel SERS substrate based on nanofingers was successfully demonstrated to provide large enhancement reliably and showed great promise for practical applications. Capillary forces bring the gold caps on the nanofingers into close proximity upon exposure to a solution containing molecules of interest, trapping molecules within the gaps and producing greatly enhanced Raman signals. Transmission electron microscopy (TEM) was used to characterize the structure of the nanofingers, in particular the gaps between finger tips to improve the fundamental understanding of the structural-performance relationship.

Nanoscale semiconductors are emerging as promising plasmonic materials for applications in the infrared. Herein, we study the near-field coupling between adjacent plasmonic resonators embedded in Si nanowires with in-situ infrared spectroscopy and discrete dipole approximation calculations. Si nanowires containing multiple phosphorus-doped segments, each with a user-programmable aspect ratio and carrier density, are synthesized via the vapor-liquid- solid technique and support localized surface plasmon resonances (LSPRs) between 5 and 10 μm. Discrete dipole approximation calculations confirm that the observed spectral response results from resonant absorption and free carrier concentrations are on the order of 10²⁰ cm^-3. Near-field coupling occurs between neighboring doped segments and the observed trends agree with plasmon hybridization theory. Our results highlight the utility of vapor-liquid-solid (VLS) synthesis for investigating the basic physics of surface plasmons in nanoscale semiconductors and suggest new opportunities for engineering light absorption in Si.

Substrate-based tuning of plasmon resonances on gold nanoparticles (NP) is a versatile method of achieving plasmon resonances at a desired wavelength, and offers reliable nanogap sizes and large field enhancement factors. The reproducibility and relative simplicity of these structures makes them promising candidates for frequency-optimized sensing substrates. The underlying principle in resonance tuning of such a structure is the coupling between a metal nanoparticle and the substrate, which leads to a resonance shift and a polarization dependent scattering response. In this work, we experimentally investigate the optical scattering spectra of isolated 60 nm diameter gold nanoparticles on aluminum oxide (Al₂O₃) coated gold films with various oxide thicknesses. Dark-field scattering images and scattering spectra of gold particles reveal two distinct resonance modes. The experimental results are compared with numerical simulations, revealing the magnitude and phase relationships between the effective dipoles of the gold particle and the gold substrate. The numerical approach is described in detail, and enables the prediction of the resonance responses of a particle-on-film structure using methods that are available in many available electromagnetics simulation packages. The simulated scattering spectra match the experimentally observed data remarkably well, demonstrating the usefulness of the presented approach to researchers in the field.

The performances of an Inverted Surface Plasmon Resonance (ISPR) biosensor based on novel materials have been studied theoretically and experimentally. The principle of ISPR is based on a maximum of reflectivity at the coupling angle instead of the common used minimum of reflectivity; this solution has not been extensively explored yet. The sensor response has been firstly simulated by the use of a dedicated Matlab routine. Different structures involving different materials have been considered and compared, in order to find the optimized solution. The metals have been deposited on a flat substrate made of optical glass. Different noble metals of optimized thickness have been then deposited on top of it. The substrates have been finally coupled with a prism to test the ISPR response. The metallic layers have been deposited at our lab by Electron Beam Evaporation. The process have been optimized for each material considered. The response of the sensors has been tested at our laboratory on a dedicated optical-bench set-up based on the Kretschmann configuration with angular modulation. The theoretical and experimental data are reported.

In this paper we investigate potential of plasmonic nano switch as a result of Fano-resonance observed in periodically arrayed silver (Ag) nanoparticles embedded over silicon (Si) on insulator (SOI) substrate, by using 3D finite difference time domain (FDTD) method. Structural parameters of the embedded silver nanoparticles were optimized giving rise to plasmon modes in the device. We find that as the device is scanned for a range of wavelength varying from visible to near infra-red, the transmission spectra exhibits Fano-line shape asymmetry for input wavelength regime near 1.3 - 1.55micron, whereas normal resonating peak is observed in the visible region. The optical properties of the switch reveal, enhancement in transmission due to strong plasmonic Fano resonance between the background and resonant processes. Sharp Fano-resonance, specific to interacting quantum systems, is exhibited by the proposed embedded hybrid design of metal nanorods into Si, which meets the condition required for high contrast switches and hence can be exploited as per anticipated results. Fano resonance in this nanorod-substrate system can also be used for designing nanoantennae, lasers, sensors, SERS etc.

Nanolasers have shown their potential in optical communication and information storage, due to their tiny footprint, potential high modulation rate and light spot under diffraction limit. In recent years, many structures use metal as whole or part of the cavity to achieve light confinement at subwavelength scale. In this paper, we propose and compare two novel types of hybrid plasmonic lasers, both with an ultrathin insulator layer sandwiched by a ring shape semiconductor and planar silver layer. The lasers differ in their cross-section curvature on the interface of metal and insulator. Finite difference time domain (FDTD) method is used to calculate and optimize these two ring laser structures. The resonant wavelength is set around 490 nm. The ultrathin thickness of the insulator layer makes photonic modes hybridize with surface plasmon plaritons (SPPs) at Ag-insulator interface, which confines the light field strongly in the ultrathin layer. The SPPs carry high momentum and high effective refractive index to TM mode. Whispering gallery mode is achieved according to strong feedback at the ring boundary by total internal reflection. The ring lasers have relatively high Q factors, approaching 100, at 250 nm radius and mode confinement around λ²/360. The mode volume can be shrunk to 0.1(λ/n)3 and 0.01(λ/n)3 respectively, which leads to Purcell factors around 70 for square cross-section and 380 for circle cross-section. We discuss the curvature effects on the mode volume and on the quality factor which accounts for the high Purcell factor for the circle cross-section.

We proposed and developed high aspect gold metasurface in order to improve the transmittance of plasmonic micro half-waveplate. Expected transmittance reaches 60% from the FDTD calculation. The metasurface is fabricated through electron beam litography (EBL) and lift-off process. Fabricated retarder was evaluated using polarization microscopy. Achieved retardation and transmittans were 144 degrees and from 25 to 40%, respectively. Four metasurface half-waveplates were arranged and applied to an ultrasmal radial polarization converter.

An exact calculation of the local electric potential field Ψ(r) in the quasi-static limit is described for the case of a point electric charge q in a composite medium where the microstructure is that of parallel flat slabs of ε₁ and ε₂ constituents. The calculation is based upon an expansion of Ψ(r) in the complete set of eigenstates of the static Maxwell equations for the electric potential in a two or three flat-slabs microstructure. In the case of an ε₂, ε₁, ε₂ three-slabs microstructure where q is in the top ε₂ layer and both ε₂ layers are infinitely thick, a perfect imaging of the point charge is expected if ε₁ = -ε₂.^1-3 The exact calculation presented here has some novel implications for the perfect imaging phenomenon.

Multiple coherent effects including Fano resonances are observed in self-assembled reduced symmetry gold nanorod systems, in particular Dolmen configurations. The bottom-up chemical method provides high quality units and assemblies (single crystal with low surface roughness and sub 5 nm gaps) that reduce radiative losses from the plasmonic structures. Multiple dark and bright plasmonic resonances are observed in optical dark-field scattering measurements and electron energy loss spectroscopy. These high fidelity structures and narrow resonances are promising for future design of high figure of merit sensors, ultrafast switches and slow light devices for optical information processing.

Transparent conducting oxides (TCOs), in general, are degenerated semiconductors with large electronic band-gap. They have been widely used for display screens, optoelectronic, photonic, and photovoltaic devices due to their unique dual transparent and conductive properties. In this study, we report in detail a technique that we developed to fabricate single crystal TCO nanorod arrays with controlled conductivity, height, and lattice spacing in a simple one-zone tube furnace system. We demonstrate how novel photonic/plasmonic properties can be obtained by selecting unique combinations of these basic parameters of the nano-rod arrays.

Colloids compound of Au/Ag nanoparticles with heterogeneous arrangement of two metals were fabricated by various techniques in the past. Laser ablation was reported as a proper technique to fabricate core/shell nanoparticles by Han et al (Appl. Phys. Lett. 92, 023116/1-023116/3 (2008)) and Chen et al (Plasmonics 7, 509-513 (2012)). The detail analysis of plasmonic properties for several metal arrangements has been done using the finite-difference time-domain (FDTD) method. The nanoparticles have been modeled as (i) core/shell nanospheres, (ii) bimetallic particles consisting of two parts (Au and Ag), or (iii) colloid consisting of pure Au and Ag nanoparticles. Results of numerical simulations show that all three investigated nanoparticle metal arrangement systems exhibit shift of the plasmonic wavelength with increase of the Ag/Au volume ratio in a similar way as recorded in the experiment. It points out that it is not possible to distinguish the metal arrangements in nanoparticles by the optical methods only and the conclusions from optical properties can be misleading. Thus optical methods can certainly prove only that bimetallic nanoparticles consist of alloy or phase separated metals.

In the present work, attempts have been made to embed Silver (Ag) /Gold (Au) - nanoparticles into polyaniline (PANI) matrix using an easy wet chemical route. It is expected that the resulting nanocomposite will show the interesting third order nonlinear optical characteristics of Ag/Au-nanoparicles modified by the advantageous properties of the conducting polymer PANI. Structural characterisation of Ag/Au-PANI nanocomposite samples was done using X-ray diffraction and Raman studies. UV-visible absorption spectra show the presence of surface plasmon resonance (SPR) peaks centred at 410 nm and 520 nm for Ag-PANI and Au-PANI nanocomposite films respectively, which is a signature of nano dimensionality of the composite samples. Third order nonlinear behaviour of the nanocomposite films was analysed using Z Scan technique employing the second harmonic output (532 nm) of a Q-switched Nd:YAG laser (Minilite, Continuum). It is seen that Ag/Au-PANI nanocomposite film samples show simultaneous presence of saturable absorption (SA) and reversible saturable absorptions (RSA) behaviour at 50 μJ laser excitation. This switching between SA and RSA has been reported in many metal nanocomposite systems. However similar behavior in nanocomposite film samples has not been pursued much. The highlight of the present work is the observation of the switching between SA and RSA in Ag/Au polyaniline nanocomposite films. The switching behavior can be ascribed to the interplay between ground state plasmon band bleaching and excited state absorption. Two photon assisted absorption has been identified as the prime factor contributing towards the observed RSA in these nanocomposite films.

We investigated optical properties of several 2D arrangements of Au nanoparticles (NPs), including dimer, trimer, hexamer, and heptamer, using finite-difference time-domain method. The heptamerous system, consisting of a central NP and six NPs forming a hexagonal shape, exhibited Fano resonance. We found that the intensity and position of the Fano resonance peak depended on the size of the central NP and its distance from the other six NPs. Furthermore we studied 3D configurations, where the location of the central NP was moved along the perpendicular direction to the plane containing the other NPs. Such vertical displacement of the central NP influenced the plasmonic coupling between NPs and affected the extinction spectra. Such 3D NP systems could provide us alternative approaches to tune the optical properties of the plasmonic NPs.

We discuss here different strategies for making arrays of Au nanoparticles using copolymer templates. Top-down and bottom-up routes are considered and the optical properties of as-prepared Au nanoparticles are discussed and compared to numerical simulations. Potential for applications such as biosensors or strain sensors is also assessed.

A novel localized surface plasmon resonance refractive index sensor based on photonic crystal fiber filled with nano-composit materials is proposed in this paper. For the introduce of a model stack of inner-silver (18nm) fused silica (220nm)silver (18nm), we can achieve more than one resonance peaks in a larger wavelength range, which make the proposed sensor possible to precisely tune the resonance wavelength to generate multiple peak shifts which can give an excellent self tunability to may be selectively used for suitable applications.

Hole arrays metallic filters can be made independent to polarization at normal incidence. However they may lose this property for a non-normal incidence, being dependent to both polar and azimuthal incident angles. These variations of the filter characteristics according to light orientation and polarization are not desirable for most optical applications. Yet, for specific geometric parameters, high-stability can be obtained for cruciform-holes Ag-SiO₂ filters. In this article, we propose a review of cross-holes metallic filters, working with CMOS-compatible materials in the visible range. We find out the main geometrical parameters impacting the filters sensitivity to the incident angles and polarization and link their role to spectral stability. We give proper design rules to realize stable filters which may lead to optical sensors with very low spectral variations whatever the incidence and the polarization of the source.

The properties of ellipsoidal nanowires are yet to be examined. They have likely applications in sensing, solar cells, microelectronics and cloaking devices. Little is known of the qualities that ellipse nanowires exhibit as we vary the aspect ratio with different dielectric materials and how varying these attributes affects plasmon coupling and propagation. It is known that the distance a plasmon can travel is further if it is supported by a thicker circular nanowire, while thinner nanowires are expected to be able to increase QD coupling. Ellipsoidal nanowires may be a good compromise due to their ability to have both thin and thick dimensions. Furthermore it has been shown that the plasmon resonances along the main axis of an ellipsoidal particle is governed by the relative aspect ratio of the ellipsoid, which may lead to further control of the plasmon. Research was done by the use of COMSOL Multiphysics by looking at the fundamental plasmon mode supported by an ellipsoidal nanowire and then studying this mode for various geometrical parameters, materials and illumination wavelength. Accordingly it was found that ellipsoidal nanowires exhibit a minimum for the wavenumber and a maximum for the propagation distance at roughly the same dimensions - Highlighting that there is an aspect ratio for which there is poor coupling but low loss. Here we investigate these and related attributes.

The arrays of metal nano-particles can support localized surface plasmon resonance (LSPR) modes, making them suitable for coloring applications. The LSPR peaks of such arrays can be tuned by changing the structural parameters, such as, shape, size, of each particle and the interparticle distance. In this paper we study the dependence of LSPR properties of arrays on the structural parameters. The extinction spectra of a spherical particle can be computed analytically using Mie theory. No analytical computation method is available for particle arrays. Numerical methods, e.g., discrete dipole approximation, finite-difference time-domain (FDTD) method are used. Here, we compute the extinction spectra of linear arrays of nano-particles using a monochromatic version of recursive convolution (RC) FDTD method. We developed this method to be able to use the handbook values of permittivity of the material of the particles at each wavelength. The simulations indicate that the position and size of the peaks of the extinction spectra are determined by the interparticle distance between any two particles and the number of particles in the array. In case of linear arrays of infinite, silver nano-cylinders, the LSPR peak can be shifted toward the longer wavelengths (red-shift) by reducing the interparticle distance. The red-shift increases as the interparticle distance becomes smaller. The peaks of extinction spectra become larger as the number of particles in the array increases.

A photochemical-based method in which UVA light (λ=366 nm) is used for synthesizing gold nanoparticles is presented by irradiating gold (III) chloride hydrate (HAuCl₄) in the presence of pharmaceutical-grade heparin sodium (PGHEP) as a reducing and stabilizing agent in aqueous solution. Different HAuCl₄ to PGHEP concentration ratios were exposed to UVA for up to seven hours. The as-synthesized nanoparticles were characterized by UV-VIS and Raman spectroscopy, transmission electron microscopy (TEM), and pH measurements. The synthesized AuNPs present spherical as well as anisotropic shapes, such as oval, triangular, hexagonal sheets, rods, and some other faceted forms, with dimensions ranging from 20 nm to 300 nm. All obtained products show good temporal stability in solution. Surface plasmons differ when varying HAuCl₄ to PGHEP concentration ratio. The obtained samples exhibit two absorption peaks, one in the region between 500-600 nm, and another one in the near-IR between 900-1200 nm; both peaks shift to longer wavelengths and increase their absorption intensity as the HAuCl4 to PGHEP concentration ratio increase. TEM images show the change in nanoparticles yield as well as the shape and sizes change depending on HAuCl₄ to PGHEP concentration ratio variation. Ph measurements suggest that acidic media promote anisotropic nanoparticle formation. Raman spectroscopy was used to find out which heparin sodium main groups attached to the nanoparticles surface, and in what amount. In summary, it is found that when modifying the reactants concentrations and keeping the UV exposition time as the only fixed parameter, different nanoparticles with distinctive characteristics can be attained.

Nanoparticles and nanostructures with plasmonic resonances are currently being employed to enhance the efficiency of solar cells. Ag stripe arrays have been shown theoretically to enhance the short-circuit current of thin silicon layers. Such Ag stripes are combined with 200 nm long and 60 nm wide “teeth”, which act as nanoantennas, and form vertical rectifying metal-insulator-metal (MIM) nanostructures on metallic substrates coated with thin oxides, such as Nb/NbO_x films. We characterize experimentally and theoretically the visible and near-infrared spectra of these “stripeteeth” arrays, which act as microantenna arrays for energy harvesting and detection, on silicon substrates. Modeling the stripe-teeth arrays predicts a substantial net a.c. voltage across the MIM diode, even when the stripe-teeth microrectenna arrays are illuminated at normal incidence.

Theoretical investigation of rotated grating coupling phenomenon was performed on a multilayer comprising 416-nmperiodic shallow rectangular polymer grating on bimetal film made of gold and silver layers. During the multilayer illumination by 532 nm wavelength p-polarized light the polar and azimuthal angles were varied. In presence of 0-35 nm, 0-50 nm and 15-50 nm thick polymer-layers at the valleys and hills splitting was observed on the dual-angle dependent reflectance in two regions: (i) close to 0° azimuthal angle corresponding to incidence plane parallel to the periodic pattern (P-orientation); and (ii) around ~33.5°/29°/30° azimuthal angle (C-orientation), in agreement with our previous experimental studies. The near-field study revealed that in P-orientation the E-field is enhanced at the glass side with p/2 periodicity at the first minimum appearing at 49°/50°/52° polar angles, and comprises maxima below both the valleys and hills; while E-field enhancement is observable both at the glass and polymer side with p-periodicity at the second minimum developing at 55°/63/64° tilting, comprising maxima intermittently below the valleys or above the hills. In Corientation coupled plasmonic modes are observable, involving modes propagating along the valleys at the secondary maxima appearing at ~35°/32°/32° azimuthal and ~49°/51°/56° polar angles, while modes confined along the polymer hills are observable at the primary minima, which are coupled most strongly at the ~31.5°/25°/28° azimuthal and ~55°/63°/66° polar angles. The secondary peak observable in C-orientation is proposed for biosensing applications, since the supported modes are confined along the valleys, where biomolecules prefer to attach.

Metallic nanobowtie is well known as a suitable structure for development of antennas that can be integrated on wide number of devices, especially in optical communications. Such feature is achieved due the presence of surface plasmon polariton (SPP) that provides a great charge density on nearby region from its tips. Considerable studies have described theoretical and experimentally the influence of gap between tips on radiation emission, once this parameter may improve the local field, as such length decrease. In optical regime, the emission enhancement is due the quantum-plasmonic interaction created from tips’ region (localized field) and the transition levels from rare earth ion of erbium (Er³⁺) and thulium (Tm³⁺). However, metallic nanobowtie with absence of gap still deserve attention, because in addition to present similar properties from regular case as previously mentioned, can also interacts with different systems, like gain materials, that can be embedded thermically into the substrate. Rare earth ion is one of the remarkable and suitable for our proposition, not only for the enhancement on measured intensity, but also its easiness to implement it on glasses, which constitute the main type of substrate adopted on plasmonic structures. In this work we performed the analysis of effects due implementation of Er³⁺ and Tm³⁺ ions into BK7 glass over a pattern of nanobowtie on absence of gap between its tips, fabricated by focused ion beam (FIB) technique from gold (Au) films. The bowties were vertically excited by an Argon laser (Ar) which wavelength ( ) is 488 nm. Furthermore, computational simulations based on finite element method (FEM), were performed to verify the dependence of nanobowtie’s geometry over the electric field along its symmetry axis.

Novel infrared superconducting nanowire single-photon detectors (SNSPD) were designed, which comprise a meandered pattern of niobium-nitride (NbN) stripes and different integrated plasmonic structures on silica substrate. To enhance absorptance of 1550 nm wavelength p-polarized light, patterns with p=264 nm periodicity were investigated, while to enhance detection efficiency, patterns with P=792.5 nm periodicity commensurate with the wavelength of surface plasmon polaritons at silica-gold interface were also designed. In OC-SNSPDs integrated with ~quarter-photonicwavelength nano-optical cavity closed by a gold reflector, the highest 63/27 % absorptance was attained in p/P-pitch design at perpendicular incidence onto NbN patterns in P-orientation corresponding to incidence plane parallel to the stripes, due to the E-field antinode at the NbN-silica interface. In NCAI-SNSPDs, where each NbN stripe is located at the entrance of a quarter-plasmon-wavelength MIM nano-cavity, enhanced 85.1/34 % absorptance is attainable in p/Ppitch design at perpendicular incidence in S-orientation, when the incidence plane is perpendicular to the integrated pattern, due to collective resonances. The maximal 95.3/70.3 % absorptances are attained at large tilting corresponding to plasmonic Brewster angles via ultra-broadband tunneling. In NCDAI-SNSPDs the longer vertical gold segments with P-pitch, which can be embedded into the silica substrate via two-step lithography, enable to attain large absorptance at small polar angles in S-orientation, due to efficient grating-coupling phenomenon. The highest 92.7/75 % absorptances are attained at 19.85°/19.35° polar angles in p/P-pitch design. P-pitch NCDAI-SNSPD supporting coupled surface waves capable of ensuring synchronous E-field enhancement below the NbN stripes is proposed for detection efficiency maximization in specific spectral-bands.

Chiral patterns are created by focused ion-beam milling nano-grooves with sub-15 nm resolution on thin metal films and arrays of nanoparticles, scattering and absorbing light selectively for left and right circularly polarized light, with high fidelity over fields up to 100 x 100 μm² without positioning errors. This allows to carry out numerical simulations to estimate light enhancement and circular dichroism both on ideal and realistic particles taken from SEM images, showing doubling of scattering cross-section and enhancement changes up to 5 times controlled by dichroism, with localized field enhancements up to 20000. 3D plasmonic structures extending out of a gold film plane are created by dry etching of the film in the openings of a resist mask defined by electron beam lithography. Conical vertical protrusions (nano-wells) are left, and their optical properties are numerically simulated, showing easily reachable out-of-plane trapping of both dielectric and metal plasmonic nano-spheres, with trapping forces up to 20 pN/W/μm². Wideband refractive index spectra in 3D-FDTD are correctly represented by overcoming the polynomial approximations to give accurate field and force/torque results for generalized artificial materials.

Nowadays, applications of surface plasmon (SP) were highlighted for facilitating the all integrated optical circuit in nano space. We introduce the design and fabrication of a periodic array of gold nanostructure for detection of light which is propagated in a SiON waveguide. The gold nanostructures are designed using Finite Element Method (FEM) and fabricated by electron beam lithography and lift-off processes. The array is composed of 5 nano rods. The nanorod has 50 nm height, 100 nm width and 15 um length. The enhancement of light at nano array was detected. Below the specific distance between nano array and waveguide, the nano array can detect the evanescent tail of light. The results demonstrate nanorods array can verify the fact that the incident light propagates in a waveguide or not when optical components are densely integrated.

The study of surface plasmon-polaritons interactions in metallic nanostructures has been a topic of interest during last years due to their use in various areas such as the photonics, chemistry and biology. Example of use is found in biosensors for the efficient detection of biological analyte and in nanophotonic elements for on-chip photonics. Here, we study the interactions properties of localized surface plasmons in a hybrid waveguiding structure made of bi-dimensional array of gold nanowires vertically integrated on silicon-on-insulator waveguides across the near infrared spectrum. With the use of near-field scanning optical microscopy (NSOM) in perturbation mode, we qualitatively obtained the spectral response of such hybrid structure through intensity near field maps of the light propagation. These experimental results demonstrate that metallic nanostructures integrated on silicon are suitable for the development of localized surface plasmon integrated devices or metallic metamaterials.