We studied the infrared properties randomly oriented silver nanowires films deposited onto different substrates. The investigated nanowires have cross-sectional diameters included between few to hundreds nanometers, while their lengths span from some microns to some tenths microns. Several films of silver nanowires were realized and the infrared emission of the obtained films was characterized in the long infrared range, i.e. 8-12 microns, by observing their temperature evolution under heating regime (maximum applied temperature ~90°) with a focal plane array (FPA) infrared camera. Under heating conditions, the apparent temperature of the silver nanowires films qualitatively follows the trend of the corresponding heating source temperature, while the absolute value keeps always somewhat lower. The experimental results show that the choice of metal filling factor may affect the resulting infrared emission and suggest that these coatings are suitable for infrared signature reduction applications.
We show both theoretically and experimentally that metal-insulator-metal resonators can be combined within the same subwavelength period and still behave independently. This permits to conceive surface with customizable absorption, which can for instance be used in dual band absorber or in omnidirectional wideband absorber. An energetic analysis can also be applied on these more complex antennas geometries, which highlights a sorting effect: at each resonance wavelength, the photons are funneled towards the apertures of the corresponding MIM cavity.
The transformation optics was introduced by J. Pendry and U. Leonhardt in 2006 [1,2]. In this method an initial space is transformed into a new space and this transformed space can be materialized by a material, which the electromagnetic parameters can be deduced from the metric of the transformed space. In the general case the electromagnetic parameters are anisotropic tensors. At microwave frequencies these materials can be realized using classical metamaterials like SRR form J. Pendry or ELC from D. Smith . At infrared wavelengths this realization is a challenge because the dimensions of the metamaterials are much smaller than the wavelength and become nanometric. Then the design of these metamaterials must be simplified and original methods must be developed to allow the realization of these metamaterials with controlled electromagnetic properties. In this paper we describe the realization of a multilayer metamaterial working at infrared wavelength, which the permittivity and the permeability can be adjusted separately. We give some examples of realized multilayer materials operating around 150THz, with a comparison between the results of full wave simulations of these materials and their characterizations using a Fourier Transform Infrared Spectrometer.
Photonic crystal metamaterial can exhibit negative index properties and this behaviour is well described by a resonator model. In this work, we present the experimental evidence that a Lorentz resonator correctly reconstruct data obtained with a negative refracting Photonic Crystal (PhC) by using a standard optical technique, such as ellipsometry. In particular we show that, in the frequency range in which the effective refractive index, neff, is equal to -1, the incident light couples efficiently to the guided modes in the top surface layer of the PhC metamaterial. These modes resemble surface plasmon polariton resonances. In add we present measurements by using standard technique of prism coupling evanescent wave. Once again the presence of localized plasmon-like modes at the surface of a silicon two-dimensional photonic crystal slab is demonstrated. Also in this case, in analogy with surface plasmons supported in metals in a photonic crystal metamaterial, the electromagnetic surface waves arise from a negative effective permittivity. These results opens new strategies in light control at the nanoscale, allowing on chip light manipulation in a wide frequency range and avoiding the intrinsic limits of plasmonic structures due to absorption losses in metals. Such negative index PhC materials may be of use in biosensing applications.
If the counterposed metal plates are vibrated, when the gap between the plates becomes narrow, the energy of stationary states between the plates increases, and when it spreads, the energy decreases. Light with the energy for this energy difference arises. This is called dynamical Casimir effect. The author has so far investigated the interaction between lattice vibration and light in a one-dimensional metal photonic crystal whose stacked components are artificially vibrated by using actuators. A simple model was numerically analyzed, and the following novel phenomena were found out. The lattice vibration generates the light of frequency which added the integral multiple of the vibration frequency to that of the incident wave and also amplifies the incident wave resonantly. On a resonance, the amplification factor increases very rapidly with the number of layers. Resonance frequencies change with the phases of lattice vibration. The amplification phenomenon was analytically discussed for low frequency of the lattice vibration and is confirmed by numerical works. The lattice-vibrating metal photonic crystal is a system of dynamical Casimir effect connected in series, and so we can expect that a dynamical Casimir effect is enhanced by the photonic band effect. In the present study, when an electromagnetic field between metal plates is in the ground state in a one-dimensional metal photonic crystal, the radiation of electromagnetic wave in excited states has been investigated by artificially introducing lattice vibration to the photonic crystal. In this case as well as a dynamical Casimir effect, it has been shown that the harmonics of a ground state are generated just by vibrating a photonic crystal even without an incident wave. The dependencies of the radiating power on the number of layers and on the wavenumber of the lattice vibration are remarkable. It has found that the radiation amplitude on lower excited states is not necessarily large and radiation on specific excited levels is large.
We describe a surface structure that possesses a different transmissivity for a surface plasmon polariton incident on it from one side of it than it has for a surface plasmon polariton incident on it from the opposite side. This asymmetric transmission of a surface plasmon polariton does not require either electrical nonlinearity or the presence of a magnetic field but is a consequence solely of the geometry of the structure. We have demonstrated that a system consisting of a square array of scatterers deposited on a metal surface in a triangular mesh to which a diffractive structure is added to the left side of it reveals asymmetric transmission when the frequency of the incident SPP is in the bandgap of the plasmonic crystal. The mechanism for this property is related to the higher Bragg modes that are excited due to the diffractive structure, while the 0-order beam, due to the existence of the band gap, is not transmitted through the structure. By varying the material and geometrical parameters of the diffractive structure one can control the contrast transmission that characterizes the degree of the asymmetry.
Propagation of light through layered metamaterials consisting of a metal-dielectric stack may be described as linear spatial filtering. We present the modelling and optimization strategy for engineering such metamaterials, as well as the measurement results of spatial filters consisting of titanium oxide and silver layers evaporated with PVD. Depending on the point spread function, the metamaterial can be applied for subdiffraction spatial filtering or for classical spatial filtering operations. We optimize the metamaterial with respect to the shape of the complex amplitude transfer function, the average transmission coefficient and to average reflections. The shape of the point spread function can only be tailored in a limited degree, due to the limited number of the degrees of freedom contained in the structure, and only in one, planarly or radially oriented dimension. The metamaterial optimised for high-pass filtering consists of several substructures, each of which is an individual cavity, and is optimized by tuning the resonance order of these cavities. In this way we obtain a high transmission for a broad range of spatial frequencies. This metamaterial can be applied to modify the contrast of the object or to introduce a phase-contrast. It may be used for far-field imaging. As an example, we propose to apply it as a novel phase-step visualization photonic element.
We present an experimental approach allowing the evaluation of the effective dielectric permittivity and magnetic
permeability of metamaterials from measurements by time-domain terahertz spectroscopy. A resonant magnetic response of TiO2 dielectric microspheres was observed in the THz range, showing that negative effective permeability can be achieved in this way. Numerical simulations explain the observed behavior, and show that by
combining the microspheres with a metallic mesh, a negative refractive index can be obtained.
Circuit model analysis extensively used to describe metamaterials response at radio and microwave frequencies needs
significant revision for application to metallic resonators in the infrared frequency range. A self consistent filament
current based approach is elaborated providing parameter values accurately describing resonators internal properties as well as inter-resonator couplings. The model is verified by comparing the excitations in a five element array obtained
from the numerical simulation using CST MWS solver with the predictions provided by the model. Although the results
presented here concern with loop like magnetic resonators, the model can also be extended to other resonator shapes, for example metallic rods.
Surface plasmon photodetectors combine metallic features on which surface plasmons may be excited with a semiconductor detector structure such as a pn or Schottky junction. The involvement of surface plasmons in detection conveys particular characteristics to the device, such as enhanced photoyield, polarisation sensitivity or spectral selectivity, which is useful for applications. An application of present interest is the detection of radiation at photon energies below the bandgap energy of silicon, particularly at optical communications wavelengths (1310 and 1550 nm), targeting optical interconnect and sensing applications. Internal photoemission on metal-silicon Schottky contacts is well-suited for this purpose as it is a broadband detection mechanism (optical and electrical). Internal photoemission is inefficient but structuring the metal forming the Schottky contact to excite surface plasmons at the metal-semiconductor interface results in an enhancement of the responsivity of the detector. Structures that exploit surface plasmons to enhance photodetection are discussed.
Interest in plasmonic lenses dates back to the seminal paper of Pendry [Phys. Rev. Lett. 85, 3966 (2000)] who has shown that superresolution is possible due to imaging through a negative-refractive-index material. Experimental verifications of near-field to near-field imaging properties of a single Ag nanolayer have proven that a resolution reaching one-sixth of the illumination wavelength is possible. The images have been recorded in a photoresist spin-coated onto an Ag layer. In this paper, images are recorded using a scanning near-field optical microscope (SNOM) working in the transmission mode with tapered-fibre metal-coated probes and aperture diameters <_ 100 nm. This recording method allows for separate recording of monochromatic images from the same lens, here we report on samples illuminated using the 404 nm mercury line. Moreover, with SNOM recording several uses of a single lens are possible. We consider dependence of the resolution on the roughness of the outer surface in the following multilayers: Ag/Ge/sapphire, Cr/sapphire, and Ag/SiO2/Cr/sapphire. Further research on reduction of chromium layer roughness is necessary.
Block-copolymer (BCP) self-assembling provides a unique tool for realizing large-area ordered metamaterials, with desired optical properties. The benefits of using BCPs as templates for metamaterials come from two main aspects: first, BCPs show a rich range of available nano-morphologies, whose domains can be conveniently tuned in size, shape and periodicity, by changing molecular parameters; second, the chemical properties of the block polymers can lead to the selective inclusion of functionalized nanoparticles (NPs) of different materials in specific nanodomains, generating periodic arrays of NPs according to the geometry of the BCP acting as template. This approach allows finely modulating the optical properties of NPs and can be used as an intriguing and versatile tool to build useful devices for Optics & Photonics applications, with significant benefits for both fundamental and applied investigations. In this work, we investigate nanostructured thin films of polystyrene-block-poly(methyl methacrylate) BCP (PS-PMMA), characterized by an hexagonal array of PS cylinders in the PMMA matrix. The PS cylindrical domain are selectively filled by functionalized metallic (Au, Ag) NPs. The optical properties of such nano-structures are strongly affected by localized surface plasmons (LSPs) in the NPs, arising from the collective resonances of conduction electrons in the metal at a characteristic spectral range, usually in the visible range. LSPs induce high field enhancement (FE), with respect to an incident light, in proximity of the NP surface, and in particular in the gap between two close NPs (hot-spot). Moreover, LSPs increase the intensity of absorption and scattering of light by the NPs in their range of resonance.
We propose and demonstrate a novel functionality of chirped mirror for monochromatic light beams: a diffraction control in reflections resulting in focusing or imaging of beams. The chirped mirrors, commonly used for manipulating temporal profiles of pulses, here are applied for manipulating the spatial dispersion of a monochromatic beam. By penetrating into dielectric layers of chirped mirror, the monochromatic beam experiences the negative diffraction, therefore the beam diverge propagating in front and behind the structure in normal diffraction region can be compensated inside this structure with negative diffraction. The result is focusing or imaging of the reflected beam from a flat interface of chirped mirror without optical axis.
Gold nanowires in general demonstrate very interesting plasmonic properties. Here, by applying the generalized Snell’s law introduced by F. Capasso in 2011, we study how the resonant behavior of the nanowires and their geometrical feature such as the radius of curvature can produce a bent in the propagation direction of a transmitted light beam. The measurements that were performed at a wavelength larger than the nanopatterned features reveal information on the meatusurface morphology.
We report on the fabrication and characterisation of fishnet structures of various dimensions on a polymer layer. The fabrication process causes metal-dielectric-metal rectangular pillars to be compressed to the bottom of fishnet structures. The metamaterial structures are fabricated using nanoimprint lithography, allowing large areas to be patterned quickly and good reproducibility through multiple use of the nanoimprint stamp. A tri-layer comprising of silver (Ag) and magnesium fluoride (MgF2) was deposited on a thick polymer layer, in this instance PMMA, before being directly imprinted by a stamp. When the metal-dielectric layered pillars are imprinted to a sufficient depth in the PMMA below the fishnet, distinct resonance peaks can be measured at both visible and near-infrared frequencies. The precise wavelength of the resonant peak at near-infrared and its Q-factor can be changed by altering the physical dimensions and number of metal and dielectric layers of the fishnet respectively. The response viewed at visible frequencies is due to the pillars that sit in the PMMA, below the fishnet. Silver and magnesium fluoride layers that comprise the suppressed pillars are crushed during the imprinting process but still allow for light to be transmitted. Despite imprinting directly into multiple metal and dielectric layers, high quality structures are observed with a minimum feature size as low as 200 nm. Resonance peaks are measured experimentally in reflectance using an FTIR spectrometer with a calcium fluoride (CaF2) beam-splitter and a visible wavelength range spectrometer with a silicon (Si) detector.
We begin to explore the possibilities offered by two-dimensional quantum metamaterials by considering the transmission across a prototypical system, that is a square array of coupled qubits (two level quantum systems). We construct a simple model that accounts for the input and detection of propagating excitations in the system. We find that even a limited degree of control through an applied field can allow the tunability between distinctly different regimes of transmission properties.
Er3+/Yb3+ co-doped BaMoO4 (BaMoO4:Er3+/Yb3+) composites with superparamagnetic iron oxide nanoparticles (SPIONs) incorporated were successfully synthesized by a cyclic microwave-assisted metathetic (MAM) method followed by heat-treatment. The microstructure exhibited well-defined and homogeneous morphology with the BaMoO4:Er3+/Yb3+ particle size of 1-2 μm and Fe3O4 particle size of 0.1-0.5 μm. The Fe3O4 particles were self-preferentially crystallized and immobilized on the surface of BaMoO4:Er3+/Yb3+ particles. The synthesized SPION/BaMoO4:Er3+,Yb3+ composites were characterized by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Optical properties were examined using photoluminescence emission measurements and Raman spectroscopy.
The Sr3V2O8 nanoparticles have been synthesized successfully using a MAS (microwave-assisted solvothermal) route followed by heat-treatment. Well-crystallized Sr3V2O8 nanoparticles with a fine and homogeneous morphology and the particle size of 100-150 nm have been formed after annealing at 600°C for 3 h. The Sr3V2O8 nanoparticles have been
characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and transmission electron microscopy. The optical properties have been investigated by photoluminescence emission and Raman spectroscopy.
In the present study will be presented granite pegmatite class of nanomaterials. For this reason it will be done a
simulations of tantalite crystals and some other tetragonal trirutile type structure of some nanomaterials having magnetic properties. Their importance is given by their magnetic properties in the paramagnetic region. In this study the growth and equilibrium forms of tantalite crystals were studied using energies . These energies were assumed to be directly proportional to the growth rate for the flat faces.
Optical metamaterials are able to achieve optical properties that do not exist in nature. Approaches to the homogenization of optical metamaterials are becoming more and more complex in the desire to achieve accurate representation. Here we propose to modify an existing retrieval approach for metamaterials to characterize their properties. To extract the effective refractive index and material parameters from reflection and transmission coefficients for double negative metamaterial in the optical regime, the modified Nicholson-Ross-Weir (NRW) method is used. In order to obtain a true picture of these metamaterials, as a function of angle of incidence of the illumination, it is important to present not only the effective parameters of permittivity and permeability but also some other important parameters such as coupling coefficients, that represent the inherent anisotropy.
The structures of double molybdates with general compositions ALn(MoO4)2 (A – alkaline metals, Cu or Tl) have been considered and compared. It has been shown that the ionic radii ratio RLn/RA is a key factor governing crystal symmetry. Different structure fields in ALn(MoO4)2 (A = Li+, Na+, K+, Cu+, Rb+, Ag+, Cs+, Tl+) molybdates have been defined as a function of element composition.
High frequencies (visible and near infrared) applications of metamaterials and plasmonic structures are strongly limited by dissipative losses in structures, due to poor conductivity of most used metals in this frequency range. The use of high temperature superconductors (HTSC) is a possible approach to this problem, being HTSC plasmonic materials at nonzero temperature. Negative dielectic constant and variety of charge carriers (electrons or holes) are further very attractive features for plasmonic applications. Characterization of the high frequency response of these materials is then necessary in order to correctly understand the optical parameters of HTSC. We report on FTIR and ellipsometry measurements on NdBa2Cu3O7-δ (Nd123) and the ruthenocuprate superconductor GdSr2RuCu2O8-δ (Gd1212) in optical and near infrared regime. Among YBCO-like cuprate superconductors, Nd123 presents the highest Tc (96K), and the most interesting magnetic response properties. Even more interesting, in view of use for metamaterial, is Gd1212, whose main characteristic is the coexistence, in the same cell, of superconductivity and magnetic order below Tc: Ru ions intrinsic magnetic moments order themselves below 135K, whereas superconductivity onset is at about 40K, depending on fabrication details. We performed measurements on Melt-Textured bulk samples, which present the best superconducting properties. Results confirm the promising feature of the considered materials; further analyses, also on powders and films, are in progress.
In this work, we present a comparative theoretical study about the optical absorption coefficient calculated in ordered nanopillar and nanohole photonic crystal silicon structures for solar energy applications. In particular, we investigate the ultimate efficiency at normal incidence condition of such structures for several fill factors and lattice constants. We find that, except for small ranges of frequency where an inversion of tendency is observed, the total absorption coefficient in nanopillar arrays is greater than the one calculated in nanohole arrays. Moreover, optimized silicon nanopillar arrays show percentage improvements of the ultimate efficiency up to 138% with respect to the case of a silicon thin film of equivalent thickness. Finally, we report preliminary experimental results about the realization of a silicon photonic crystal with a nanopillar array structure to be exploited as an optical trapping film in solar cells.