Calculation Of Refractive Index Research Articles

Aerosol absorption and radiative forcing

Abstract. We present a comprehensive examination of aerosol absorption with a focus on evaluating the sensitivity of the global distribution of aerosol absorption to key uncertainties in the process representation. For this purpose we extended the comprehensive aerosol-climate model ECHAM5-HAM by effective medium approximations for the calculation of aerosol effective refractive indices, updated black carbon refractive indices, new cloud radiative properties considering the effect of aerosol inclusions, as well as by modules for the calculation of long-wave aerosol radiative properties and instantaneous aerosol forcing. The evaluation of the simulated aerosol absorption optical depth with the AERONET sun-photometer network shows a good agreement in the large scale global patterns. On a regional basis it becomes evident that the update of the BC refractive indices to Bond and Bergstrom (2006) significantly improves the previous underestimation of the aerosol absorption optical depth. In the global annual-mean, absorption acts to reduce the short-wave anthropogenic aerosol top-of-atmosphere (TOA) radiative forcing clear-sky from −0.79 to −0.53 W m−2 (33%) and all-sky from −0.47 to −0.13 W m−2 (72%). Our results confirm that basic assumptions about the BC refractive index play a key role for aerosol absorption and radiative forcing. The effect of the usage of more accurate effective medium approximations is comparably small. We demonstrate that the diversity in the AeroCom land-surface albedo fields contributes to the uncertainty in the simulated anthropogenic aerosol radiative forcings: the usage of an upper versus lower bound of the AeroCom land albedos introduces a global annual-mean TOA forcing range of 0.19 W m−2 (36%) clear-sky and of 0.12 W m−2 (92%) all-sky. The consideration of black carbon inclusions on cloud radiative properties results in a small global annual-mean all-sky absorption of 0.05 W m−2 and a positive TOA forcing perturbation of 0.02 W m−2. The long-wave aerosol radiative effects are small for anthropogenic aerosols but become of relevance for the larger natural dust and sea-salt aerosols.

Negative refractive index in the near‐UV from Au‐coated CuCl nanoparticle superlattices

AbstractNanoparticle superlattices consisting of CuCl spheres coated with a gold (Au) nanoshell are shown to exhibit negative index of refraction in the near‐UV regime. These predictions are based on calculations of the effective refractive index by use of the extended Maxwell–Garnett theory. The results for the refractive index are supplemented by multiple‐scattering calculations of light‐transmittance curves from finite slabs of nanoparticle superlattices. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Some remarks on the calculation of the complex refractive index of medium in terahertz reflection spectroscopy

AbstractThis paper presents a technique, based on dispersion theory, for the analysis of terahertz reflection spectroscopy data measured using ellipsometric methods. Formulas for the complex reflection coefficient provide simpler equations than those used in conventional ellipsometry for resolving the complex refractive index in the THz spectral range. It is proposed that a reflection coefficient ratio yields information on the surface roughness when probing a surface by THz radiation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A quantitative structure-property relationship study for refractive indices of conjugated polymers

The quantitative structure-property relationship (QSPR) study was performed between descriptors representing the molecular structures and refractive indices for a set of 35 pi-conjugated polymers. A seven-descriptor correlation was developed for the prediction of refractive indices with R = 0.936 and s = 0.028 by stepwise multilinear regression analysis. The average relative error for the calculation of refractive indices was 1.022%. The stability of the proposed model was validated using leave-one-out cross-validation and randomization experiments. Since the model requires only molecular descriptors derived solely from the repeating unit structures of conjugated polymers, it has better predictive capability comparing with the existing group-contribution methods.

Many-Body Calculations of Dynamic Polarizability, Refractive Index and Verdet Coefficient

Within the framework of the many-body theory by using the Random Phase Approximation with Exchange (RPAE) method we calculated the frequency dependent polarizability, refractive index, and Verdet coefficient of some atoms. Calculated time-dependent peculiarities of a set of atoms are very significant in the nano-region and might be important for designing new materials.

Calculation of the negative refractive index of a LHM slab by the free-space mapping of the laterally shifted refracted beam

In this paper, we present a novel method to calculate the effective negative refractive index of a left-handed material (LHM)—a composite of split-ring resonators (SRRs) and thin wire structures. A LHM slab was first fabricated and then the measured transmission and reflection results were used to determine the LHM passband. To obtain the effective negative-refractive index, a microwave beam was obliquely launched to illuminate the slab for which a 2D spatial-field profile of the refracted beam outside the slab was obtained by scanning the lateral shifting of the field with respect to normal for a band of frequencies. A lateral shift of the refracted beam towards the same side of the incident beam for the LHM passband confirmed negative refraction in the LHM slab and the refractive index calculated for that frequency region was conclusively negative according to Snell's law. The presented method provides an alternate and efficient way to measure the effective refractive index of a LHM. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 593–596, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21417

Out-of-plane dispersion and homogenization in photonic crystal slabs

We report a measurement of out-of-plane dispersion in two-dimensional photonic crystal slabs. Using terahertz time-domain spectroscopy, we obtain the complex transmission coefficient over a broad spectrum, ranging from the long wavelength (homogeneous) limit up to beyond the first few guided resonances. Despite the absence of a band gap, the out-of-plane dispersion is significant and in addition exhibits a complicated spectral dependence. Calculations of the effective refractive index which assume translational invariance in the direction perpendicular to the slab are in only approximate agreement with the measured homogeneous effective index and dispersion. In contrast, numerical simulations which accurately account for the finite slab thickness give much more accurate predictions.

ICRF heating in volumetric neutron source JUST-T for transmutation of minor actinides

Plasma heating by waves in the cyclotron frequency range (ICRF) in parallel with neutral beams is proposed for the volumetric neutron source based on the JUST-T tokamak project. Calculations of the transverse refractive index ( ) were performed for slow waves (SW) and fast magnetosonic waves (FW) versus the plasma radius. The coefficients of SW and FW decay for ICRH at the harmonics of the ion-cyclotron frequency and for ions and electrons were calculated. The calculations were performed for three DT mixtures: (a) deuterium minority in tritium plasmas; (b) n D∼ n T; and (c) tritium minority in deuterium plasmas. The calculations were also performed for 3He minority in DT plasmas with comparable D and T concentrations. The effective formation of travelling fast waves in VNS JUST-T by phasing several loop antennas located some distance away in the toroidal direction to provide current drive is investigated.

Calculations of Nonlinear Refractive Index of Alkali Halides

Theoretical values of the nonlinear refractive index n2 of 16 rock salt-structure alkali halides are presented. The approach employed is based on the Phillips–Van Vechten interpretation of the bond polarizability model. Our results show that in halides with the same cation a monotonic, strong increase in n2 with the linear refractive index can be observed.

Theoretical Calculations of Refractive Indices and Optical Effects in Spectra of Nitric Acid and Nitric Acid Monohydrate Crystals

The theoretical infrared refractive indices of two systems related to atmospheric research, nitric acid (NA) and nitric acid monohydrate (NAM) crystals, have been computed using a methodology based on first-principles. The effects of lack of coherence in the infrared beam in RAIR and transmission spectra have also been treated using a model based on classical optics. The optical constants of NA crystals are presented for the first time; the results on NAM are compared to empirical values previously published with good general agreement. With the optical constants of NA, polarized reflection-absorption infrared spectra are predicted and compared to experimental spectra recorded also for the first time, for a set of varying film thickness. The global agreement is satisfactory. The effects of a number of experimental factors in transmission spectra of NAM are assessed, in an attempt to explain observed differences among experimental spectra. It is concluded that the spectral disparities are probably due to differences in the nature of the samples.

Verification and Calculation of Negative Refractive Indices ofa Meta-Material by Numerical Method

The verification and calculation of the negative refractive index of ameta-material is carried out by the finite-difference time-domainmethod. A slab and a prism of the meta-material are simulated. Agenuine plane wave is generated by a two-direction periodic boundarycondition (PBC) in the slab model. Based on an advanced phaseextraction technique, the negative refractive index of themeta-material is verified by phase velocity measurement in the slab andprism measurement. From our results, not only the phenomenon ofbackward phase propagation but also the negative refraction is clearlyobserved. The index is also calculated precisely. The results from thetwo models are consistent.

Properties of modified cyclo-olefin copolymers predicted by ab initio and molecular simulation techniques

Mechanical, thermal and optical properties of modified cyclo-olefin copolymers COC were studied by molecular dynamics simulations and ab initio calculations. The COC chains were modified by substituting the norbornane rings with methyl groups and replacing ethane units with propane. A modified Dreiding 2.21 force field was developed for the molecular dynamics simulations. The bulk and Young’s moduli increased when the norbornane rings of COC were substituted with methyl groups and when the ethane units were replaced with propane. The highest glass transition temperature was obtained when the norbornane rings were substituted with methyl groups. Ab initio calculations of isotropic polarizability and refractive index were sensitive to the applied basis set and level of theory. Good agreement with available experimental data was obtained with the B3LYP/6-311G** method. Replacement of ethane units with propane lowered the refractive index significantly, whereas other structural modifications had practically no effect.

Absolute optical rotation of CsLiB6O10

The optical rotation (OR) of CsLiB6O10 (CLBO, space group I\bar{4}2d) along the a axis has been determined by the HAUP method [Kobayashi & Uesu (1983). J Appl. Cryst. 16, 204–211] at a wavelength of 632.8 nm and by the TILTER method [Kaminsky & Glazer (1996). Ferroelectrics, 183, 133–141] at 532 nm and 650 nm. The respective rotatory powers were found to be 17 (1), 24 (2) and 19 (2)° mm−1. The absolute chirality has been established by comparing Bijvoet differences, {hkl} and {k\bar{h}l}, on the same crystal on which OR was measured. Atomic positions and electron density Fourier peak heights were exploited as input for semi-empirical calculations of refractive indices and OR, using WinOPTACT [Glazer (2002). J. Appl. Cryst. 35, 652] with only one free parameter fitted to match the average refractive index.

Convective Deposition of Silica Nano-Colloidal Particles and Preparation of Anti-Reflective Film by Controlling Refractive Index

Anti-reflection film was coated by using spherical silica nano colloids. Silica colloid sol was reserved between two inclined slide glasses by capillary force, and particles were convectively stacked to form a film onto the substrate as the water evaporates. As the sliding speed increased, the thickness of the film decreased and the wavelength at the maximum transmittance decreased. The microstructure observed by SEM showed that silica particles were nearly close packed, which enabled the calculation of the effective refractive index of the film. The film thickness was measured by proffer and calculated from the wavelength of maximum transmittance and the effective refractive index. The effective refractive index of the film could be controlled by a subtle controlling of the coating speed and by mixing two different sized silica particles. When the 100 nm and 50 m particles were mixed at 4:1-5:1 volume ratio, the maximum transmittance of <TEX>$95.2\%$</TEX> for one-sided coating was obtained. This is the one that has increased by <TEX>$3.8\%$</TEX> compared to bare glass substrate, and shows that <TEX>$99.0\%$</TEX> of transmittance or <TEX>$1.0\%$</TEX> of reflectance can be achieved by the simple process if both sides of the substrate are coated.

Calculations of band-filling optical nonlinearities in extrinsic semiconductors beyond the low injection limit

Theoretical calculations of room temperature band-filling optical nonlinearities in a bulk semiconductor are reported. The approach, based on self-consistent determination of pseudochemical potentials, improves on other existing calculations as it correctly takes into account an arbitrary optical injection level. The self-consistent approach also enables direct calculation of the nonlinear optical susceptibility without fixing the photogenerated electron-hole density as a parameter, as required in existing phenomenological models. Good agreement with experimental results is obtained, in the case of GaAs, when photoexcited carrier densities above the Mott transition are considered. Calculations of pair density and nonlinear refractive index are shown as a function of the doping level and of the pump intensity for bulk GaAs. Finally, the limits of the model and applications to calculations of optical behavior in more complex structures are discussed.

Theoretical Study of Temperature Tuning and Anisotropy of Liquid Crystal Infiltrated Synthetic Opal as Photonic Crystal

We have theoretically studied the occurrence of photonic band gap. Calculated values of relative width and lattice size for nematic liquid crystal ZLI-1132 and smectic ferroelectric liquid crystal (R)-4′-(1-methoxycarbonyl-ethoxy)-phenyl-4-[4-(n-octyloxy)phenyl]benzoate (1MC1EPOPB) synthetic opal (SiO2) infiltrated with liquid crystal as a function of temperature using a model of strong localization for the occurrence of pseudogap are reported for the W-point in the Brillouin zone. A new expression for refractive index calculation for synthetic opal infiltrated with liquid crystal is proposed. Central wavelength is also calculated and compared with the observed ones. The structure parameter and opal size are also given. This work is important for temperature tuning and anisotropy of photonic crystal.

The shape of the aging human lens: curvature, equivalent refractive index and the lens paradox

Scheimpflug slit images of the crystalline lens are distorted due to the refracting properties of the cornea and because they are obliquely viewed. We measured the aspheric curvature of the lens of 102 subjects ranging in age between 16 and 65 years and applied correction for these distortions. The procedure was validated by measuring an artificial eye and pseudophakic patients with intraocular lenses of known dimensions. Compared to previous studies using Scheimpflug photography, the decrease of the radius of the anterior lens surface with age was smaller, and the absolute value for the radius of the anterior and posterior lens surface was significantly smaller. A slight decrease of the posterior lens radius with age could be demonstrated. Generally, front and back surfaces were hyperbolic. Axial length was measured of 42 subjects enabling calculation of the equivalent refractive index of the lens, which showed a small, but highly significant decrease with age. These new findings explain the lens paradox and may serve as a basis for modelling the refractive properties of the lens.

Calculation of refractive indices and local electric field tensors in α-sexithiophene crystal

Polarizabilities calculated for sexithiophene using Hartree–Fock and density-functional approaches with a 6-31G ∗ basis set are used to calculate refractive indices and local electric field tensors in the α-sexithiophene crystal. The calculations under-estimate the (incomplete) experimental refractive indices but polarizabilities are devised that fit them. These predict that the unknown refractive index perpendicular to the crystal bc plane is larger than those in the plane. The tilted molecular long axis produces sizeable off-diagonal local-field components in the crystal ac plane. This complicates the analysis of electro-absorption spectroscopy.

Calculation of refractive indices and third-harmonic generation susceptibilities of liquid benzene and water: Comparison of continuum and discrete local-field theories

The refractive indices (linear response) and the nonlinear susceptibility for third harmonic generation (THG) at λ=1064 nm of liquid water and benzene are predicted, using ab initio molecular (hyper)polarizabilities and local-field corrections calculated according to the Lorentz model, the generalized reaction-field model of Onsager, and a discrete local-field theory applied to liquid structures obtained by classical molecular simulation methods. The ratio of the calculated THG susceptibilities for the two liquids is compared with experimental results, in order to avoid ambiguities concerning the factors used to calibrate the THG experiments. All models are able to reproduce the experimental refractive indices of both liquids accurately, but are less successful for the THG susceptibility. The discrete local-field corrections for the THG susceptibility are considerably larger than those of the continuum model in the form of the more accurate extended reaction-field approach.

Analysis of Sub-Micron Spherical Particles using Scanning Flow Cytometry

Determination of individual sub-micron particle size and refractive index was performed with a parametric solution of the inverse light-scattering problem. The parametric solution is based on approximating equations that relate the particle characteristics to the parameters of the indicatrix (an angular dependence of light-scattering intensity). The approximation equations allow real-time calculation of particle size and refractive index ranging from 0.5 to 1.5 μm and from 1.37 to 1.69, respectively. The applicability of the parametric solution was demonstrated with the analysis of polystyrene particles, the indicatrices of which were measured using scanning flow cytometry. We measured samples of monodisperse polystyrene particles with diameters of 0.6 and 0.83 μm. The measured indicatrices were processed with the parametric solution and best-fit regression to the Mie theory. The determined particle parameters were in a good agreement with the specifications.