Behavior Of Refractive Index Research Articles

Optical and structural properties of poly(vinyl alcohol) films embedded with citrate-stabilized gold nanoparticles

Hydrosol of Au nanoparticles was prepared by citrate reduction of chloroauric acid. The synthesized nanoparticles were characterized through transmission electron microscopy (TEM) and UV–Visible spectroscopy. The prepared nanoparticles were almost spherical in shape with their mean diameter ∼6 nm and possessed face-centred-cubic (fcc) structure. The absorption spectrum of the as-prepared nanoparticles shows the SPR peak at 530 nm in agreement with that predicted from calculations based on Mie theory. These nanoparticles were dispersed in poly(vinyl alcohol) (PVA) using the sol–gel method to prepare PVA–Au nanocomposite films with different concentrations of Au. Optical and structural properties of these nanocomposites were studied using UV–Visible spectroscopy, x-ray diffraction (XRD) and FTIR spectroscopy. The value of optical band gap deduced from the UV–Visible absorption spectroscopy is found to be reduced from 4.98 eV (for pure PVA) to 3.85 eV after embedding 0.074 wt% of Au nanoparticles. Further, the refractive index behaviour for pure PVA and PVA–Au nanocomposite films was studied through transmission and reflection behaviour. The induced structural changes, revealed through XRD and FTIR spectroscopy, are responsible for the observed changes in optical behaviour of PVA after embedding Au nanoparticles in it.

NEGATIVE REFRACTIVE INDEX BEHAVIOR THROUGH MAGNETO-ELECTRIC COUPLING IN SPLIT RING RESONATORS

An investigation on the possibility of obtaining a negative refractive index behavior in split ring resonators (SRRs) through magneto-electric coupling is presented. We have performed rigorous electromagnetic simulations using a full-wave 3D simulator, and the obtained results have been verifled by our experimental realizations and measurements. The results conflrm that the increase of magneto- electric gyrotropic activity inside a bi-anistropic medium can lead to the establishment of backward-wave propagation.

Quantized Energy Momentum and Wave for an Electromagnetic Pulse—A Single Photon inside Negative Refractive Indexed Media

An Electromagnetic (EM) radiation in dispersion less free space vacuum is represented by a photon, with corpuscular and wave nature. The discussions, for the past century aimed at the nature of photon inside a media having dispersion in the refraction property, other than free space. What about its nature if the space be of refractive index which is negative, is discussed in this paper. We call mechanical momentum, wave-momentum, and try to match our present theories with intriguing property of this ‘photon’ or pulse carrying EM energy packet, and more so we try to find its property energy, momentum inside a media a positive refractive media, and if the media show a negative refractive index behavior, then these queries are profound, and suitable explanations to these classical concepts of corpuscular-wave nature of photon inside these media are quest for the scientists dealing with these materials having negative index of refraction. Here some of this counterintuitive nature of corpuscular-wave nature of photon inside negative indexed material is brought out, with possible ‘new definition’ of its ‘wave-momentum’, the concept of ‘reactive energy’ inside negative indexed material, along with possible ‘new wave equation’. These definitions and expressions of ‘wave-momentum’ and ‘reactive energy’ pertaining to negative indexed material are new and discussed and derived by classical means.

Linear and nonlinear refractive index of As–Se–Ge and Bi doped As–Se–Ge thin films

The present work reports the linear and nonlinear refractive index for (As2Se3)90Ge10 and [(As2Se3)90Ge10]95Bi5 thin films. The formulation proposed by Fournier and Snitzer has been used to predict the nonlinear behavior of refractive index. The linear refractive index and Wemple–DiDomenico parameters were used for the determination of nonlinear refractive index in the wavelength region 0.4 to 1.5 μm. Linear refractive index has been determined using the well known Swanepoel method. This is observed that nonlinear refractive index increases linearly with increasing linear refractive index. With Bi addition this has been found that nonlinear refractive index increases by 2.4 times, while on comparing with pure and doped silica glasses results are 2–3 orders higher. Density and molar volume has also been calculated. The obtained results may lead to yield more sensitive optical limiting devices and these glasses may be used as an optical material for high speed communication fibers.

Structure and optical properties of CuAlS_2 thin films prepared via chemical bath deposition

CuAlS_2 thin films of thicknesses 118 \pm 5 nm were deposited on glass substrates using chemical bath deposition technique. The details of the preparation method are well described. The method is relatively simple and is easily controlled and sufficient to produce large area and good adherence to the substrate films. Effect of annealing temperature T_a on the structure, and optical properties of CuAlS_2 films were investigated. The structures of the films were studied by X-ray diffraction and FTIR spectrophotometer. The optical properties of the films were ascertained by UV-VIS spectrophotometer (wavelengths ranging between 300 and 900 nm). The optical transmittance and absorption were utilized to compute the absorption coefficient, band gap energy and optical constant of the films. Nature of the optical transition of the films has been observed in direct allowed with band gap energies between 2.81 eV and 2.4 eV depending on annealing temperatures. The refractive index and extinction coefficient behavior were found to very affect by annealing temperature.

Theory of electromagnon resonances in the optical response of spiral magnets

The optical response of spiral magnets is studied, with special attention to its electromagnon features. We show that these features trace back to the resonant magnetoelectric response resulting from the spiral ordering (irrespective of any concomitant ferroelectricity). This response, being magnetoelectric in nature, not always can be reduced to an effective electric permittivity. We argue that electromagnons in spiral magnets can produce, in addition to the observed peaks in the optical absorption of multiferroics, a (dynamically enhanced) optical rotation and a negative refractive index behavior.

Influence of nanoparticles on elastic and optical properties of a polymeric matrix: Hypersonic studies on ethylene–vinyl alcohol copolymer–titania nanocomposites

High resolution Brillouin spectroscopy (HRBS) backscattering elastic data in nanocomposites of ethylene–vinyl alcohol copolymer (EVOH) and TiO 2 nanoparticles present anomalous dependence with concentration, while Young’s modulus and microhardness data show the expected behaviour. When performing HRBS with the 90A scattering geometry to asses the effective elastic constant, the expected behaviour for low concentration of TiO 2 nanoparticles is again obtained. This unusual disagreement can be solved assuming that the inclusion of TiO 2 nanoparticles induces anomalous refractive index behaviour at the applied laser wavelength for the different EVOH–TiO 2 nanocomposites. Comparison with experimental elastic and optical data obtained in isotactic-polypropylene–TiO 2 nanocomposites proves that EVOH–TiO 2 nanocomposites show an unusual optical behaviour at the laser wavelength, possibly due to a singular bonding between the EVOH polymer and the TiO 2 nanoparticles.

Holey metal films: From extraordinary transmission to negative-index behavior

In this paper we study the common physical background of the phenomenon of extraordinary optical transmission in holey metal films and the emergence of the negative refractive index behavior in double fishnet structures. Here we provide further evidence that the resonant magnetic response of the latter structures is associated with the excitation of gap surface plasmon modes. The evolution of the optical response with the number of double fishnet layers is also addressed, finding that the effective refractive index reaches a converged value for a moderate number of layers.

Single- and double-negative refractive indices of combined metamaterial structure

We experimentally and numerically studied the transmission spectra of a combined metamaterial structure whose negative refractive index was supposed to be achievable only with simultaneously negative permittivity and permeability. However, it was found that the negativity of the refractive index of such a structure could be obtained not only when both parameters were negative but also when only one parameter, more specifically the permittivity was negative. These characteristics of combined structure were analyzed in detail by using the standard retrieval effective-medium method. According to the analyses, it can be concluded that the negativity originates from the complex permittivity and permeability. The interplay among the real and the imaginary parts of those parameters is the key to the negative behavior of refractive index.

Refractive-index dispersion of glassy semiconductors in the pseudo-binary As 2Se 3–SbSI system

The bulk chalcogenide glasses in the pseudo-binary system (As 2Se 3) 100− x (SbSI) x (with x = 20, 30, 50, 70 and 80 at.%) were prepared from high-purity elemental components by melt-quenching technique. It is a system with the variable ratio of classical amorphous compound As 2Se 3 and the molecule of antimony-sulphoiodide, SbSI, which in the monocrystal form is characterized as a ferroelectric. The refractive-index behaviour (magnitude and spectral dispersion) of investigated glasses was determined by the prism method and analyzed. To calculate and discuss the parameters of dispersion in the band gap region three different approaches were used (Cauchy, Sellmeier and Wemple–DiDomenico single-oscillator model). The comparison of the results shows good agreement between all applied models. It was found that the value of the refractive-index shows normal dispersion behaviour and increases with the increase of Sb (or SbSI) content in the investigated system, whereas the optical gap of these glasses E g slightly decreases.

Wideband high‐gain antenna using metamaterial superstrate with the zero refractive index

AbstractA high‐gain antenna using a single layer metamaterial (MTM) superstrate with a zero refractive index (n) is proposed. To enhance the magnitude and flatness property of the antenna gain at the same time, the effectively zero refractive index behavior of metamaterial superstrate is used, which gathers the wave emitted from the microstrip patch antenna and collimates it toward the normal direction of the antenna. Both the simulation and measurement results provide that the realized gain of the proposed antenna is increased by about 5 dB and the flatness of that gain is no more than 1.5 dB in the predicted frequency band, where the proposed MTM is designed to have a zero index of refraction. Consequently, the high and flat gain antenna can be easily obtained by using our MTM superstrate. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1973–1976, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24469

Novel Planar Metamaterial with a Negative Refractive Index

A new planar metamaterial (MTM) with simultaneous negative values of permittivity (e) and permeability (μ) is proposed. Our MTM is composed of two identical copper patterns etched on both sides of dielectric laminate, which is very thin and easy to fabricate. Unlike conventional MTMs, the proposed structure shows a negative refractive index (NRI) behavior with respect to a normally incident wave. To explain the underlying principle of the NRI characteristics, an equivalent resonant circuit model based on surface current density distribution is investigated. An eigenmode analysis and a three-dimensional wave simulation for the stacked MTM prism are also performed to verify the existence of negative refraction. The experimental results from the transmission and reflection measurement ensure the validity of our design approach and show good agreement with the theoretically predicted effective medium parameters. Keywords ⎯Negative refractive index (NRI), metamaterial, effective medium parameter.

Non-Resonant Third-Order Nonlinearity of Nanometric and Subnanometric Silver Particles in Aqueous Solution

We have measured and analyzed the behavior of the nonlinear refractive index of silver spheres in water in a non-resonant femtosecond excitation regime. Two different diameter silver nanosphere (0.65 and 9 nm) suspensions were used in the experiments. Thermal and nonthermal contributions to the nonlinear properties of the samples were determined exploring a novel high sensitivity thermal managed eclipse Z-scan technique. The dependence of nonthermal third order nonlinear susceptibility of the colloid with the silver nanoparticles filling factor was described using the generalized Maxwell-Garnett model. The nanoparticle size dependence of the colloid nonlinear refractive index was observed.

Performance of Canola (Brassica napas L.) Seed Yield, Yield Components and Seed Quality under the Effects of Four Genotypes and Nitrogen Fertilizer Rates

Abstract. This study was conducted at the Agricultural Research Station, Hada El-Sham, King Abdulaziz University during 2006 and 2007 seasons. Four canola varieties, Callypso, Pactole, Sero-4 and Sero-6 varieties were tested under four nitrogen fertilizer rates (0.00, 92,138 and 184 kg N/ha) to determine the effect of nitrogen fertilizer on the canola (Brassica napus L.) seed yield, yield components and seed quality. The results showed that as nitrogen fertilizer rate increased, plant height, number of fruit / plant, 1000-seed weights, seed weight / plant and protein content increased. However oil content (%), was the highest under 92 kg nitrogen rate, then significantly decreased under the higher nitrogen rates. In terms of variety differences, the plant height data revealed that Sero-4 was the taller, followed by Sero-6, and then Callypso and Pactole varieties and Pactale and Sero-6 varieties produced the highest number of fruits/ plant and significantly dominated over the Sero-4 and Callypso variety. In addition, Pactale and Sero-4 had the highest 1000-seed weights without significant differences between them, while Callypso variety was the lowest. Pactole variety was also the highest in seed weight / plant, while Sero-4 and Sero-6 varieties were not significantly different in seed weight / plant. Pactole variety was the highest in protein content followed with a significant difference by Sero-4, then Sero-6, while the lowest variety in protein content was Callypso variety. The rate of 138 kg N / ha produced the highest seed yield / ha (1550.51 kg), protein content (28%) and had 34.10% oil content. Oil content of the studied varieties ranged from 37.80% for Callypso variety to 32.04% for Sero-4 variety, and the statistical comparisons showed significant differences among the four studied varieties. Furthermore, iodine value and refractive index of the oil under the effects of nitrogen fertilizer rates were not significantly different from each other and the same behavior of iodine value and refractive index

Volumetric, ultrasonic, viscometric and refractive index behaviour of binary mixtures of styrene with ethylalcohol and chlorobenzene at different temperatures ( T = 298.15 K to 313.15 K)

This paper presents experimental data for densities, ρ, viscosities, η, ultrasonic speeds, u, and refractive indices, n, of pure styrene (STY), chlorobenzene (CB), ethylalcohol (EA) and of their binary liquid mixtures over the entire composition range at 298.15, 303.15, 308.15, 313.15 K. The uncertainties in density, ultrasonic speed, viscosity, and refractive index measurements are ± 0.0001 g cm − 3 , ± 0.15 m s − 1 , ± 0.003 mPa s, and ± 0.0002 units, respectively. From these experimental data, excess molar volume, deviations in isentropic compressibility, viscosity and in refractive index and internal pressure are calculated for all the binary mixtures, over the entire composition range. The apparent molar volume, V ϕ ,2, and apparent molar compressibility, K ϕ ,2, of CB and EA in styrene were also calculated. Partial molar volume, V− ϕ ,2 0, and partial molar compressibility, K− ϕ ,2 0, were estimated by using the values of V ϕ ,2 and K ϕ ,2 of CB and EA in styrene at infinite dilution. The excess and deviation functions were fitted to Redlich and Kister type polynomial equation. Moreover, theoretical predictions of refractive index of the two binary mixtures are made on the basis of empirical and semiemperical relations by using the experimental values of the pure components. The results provide information on the molecules in the pure liquids as well as in the binary mixtures.

Plasmonic metamaterials based on holey metallic films

In this paper we address from the fundamental point of view the links and relationsbetween three different phenomena that emerge when metallic films are perforated withperiodic arrays of holes: (i) the phenomenon of extraordinary optical transmission in singlemetallic layers, (ii) the appearance of surface electromagnetic modes (the so-called spoofsurface plasmons) when an array of holes is drilled on the surface of a perfectelectrical conductor and (iii) the negative refractive index behavior observed indouble-fishnet (DF) structures in which a periodic hole array is perforated on ametal–dielectric–metal stack. By using a very simple theoretical framework, we showhow the physical origin of the negative refractive index in these DF structures isdue to the excitation of spoof gap surface plasmon modes that propagate withinthe dielectric slab. We also demonstrate that the electrical response of the DFsystem is mainly controlled by the cut-off frequency of the hole waveguide. Finally,we present some results for multilayered DF structures that illustrate how thenegative refractive index is maintained when several DF units are stacked together.

Optical properties of TiO2 films made by air oxidation of Ti

AbstractIn this work spectral behaviour of complex refractive index of thermal oxidized titanium films deposited onto Si (100) substrate were investigated by spectroscopic ellipsometry in the range of 1.5‐4.77 eV. The films were subjected to annealing in air at temperature 750 °C for 7 and 25 hours. As it follows from our studies, air oxidation of titanium resulted in coexisting of different phases in the film, and dependence of their optical and structural properties upon z‐coordinate (upon film depth). The spectral dependences of complex refractive index and the changing of film thickness due to cumulative annealing were determined from pseudodielectric function (PDF) ‐ ε(E) spectra, for which data acquisition was performed by Spectroscopic Phase Modulated Ellipsometer (SPME). Complicated phase composition of films was revealed by using multi‐layers conception of investigated film and applying oscillator's model and EMA approximation for description of spectral dependence of dielectric function of film or its separate layers. Raman spectra were used to distinguish phase components in the films. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Relationship between biaxial orientation and oxygen permeability of polypropylene film

Biaxially oriented polypropylene (BOPP) films were produced by simultaneous and sequential biaxial stretching to various balanced and unbalanced draw ratios. The BOPP films were characterized in terms of density, crystallinity, refractive index, oxygen permeability and dynamic mechanical relaxation behavior. It was found that the density and crystallinity of BOPP films decreased as the area draw ratio increased. Sequential stretching led to a slightly lower density than simultaneous stretching to the same draw ratio. Moreover, sequential stretching produced lower orientation in the first stretch direction and higher orientation in the second stretch direction compared to simultaneous stretching. The study confirmed the generality of a one-to-one correlation between the oxygen permeability of BOPP films and the mobility of amorphous tie chains as measured by the intensity of the dynamic mechanical β-relaxation. Moreover, the study established the correlation for commercially important sequentially drawn BOPP films with an unbalanced draw ratio. Finally, the chain mobility in the stretch direction was found to depend on the final stress during stretching.

On the refractive index of ageing dispersions of Laponite

Aqueous dispersion of Laponite at low ionic concentration is of interest since it undergoes structural evolution with respect to time, which is usually termed as ageing. In this work we study the refractive index behavior as a function of ageing time, concentration and temperature. We observed that the extended Lorenz–Lorentz equation fitted the refractive index dependence on concentration and temperature very well. The refractive index did not show any dependence on ageing time. However, the dependence of refractive index on concentration showed a marked change as the system underwent transition from an isotropic to a biphasic state. The slope of the refractive index–density data is remarkably close to that of water at all Laponite concentrations. In the context of transport phenomena, optical measurements such as interferometry can exploit the water-like behavior of Laponite dispersions.

Refractive index behavior in phosphate glass from the view point of B3+ and Al3+ coordination

Higher refractive index and higher Abbe value were obtained simultaneously at B2O3/Al2O3=1 in the system of 65P2O5–xAl2O3–(20−x)B2O3–10CaO–5Li2O, although the refractive index generally shows a positive correlation with the dispersion. We investigated the molar volume and the molar refraction by Lorentz–Lorenz’s formula and also studied the coordination number of 11B and 27Al by MAS NMR. By the replacement of Al2O3 with B2O3, the molar refraction constantly decreased, but the molar volume was minimized at B2O3/Al2O3=1. The refractive index behavior of the glasses was mainly determined by the molar volume in the system. The coordination number of B3+ was only IV and it did not change if the composition was changed. On the other hand the coordinations IV, V and VI were observed for Al3+. The ratio of Al3+(VI) was maximized at B2O3/Al2O3=1. It is considered that the higher coordination of Al3+ brings the improvement of the packing and it leads to high refractive index.