Choice Of Refractive Index Research Articles

Accounting for black carbon refractive index in atmospheric radiation

AbstractBecause of the fractal aggregated structure of black carbon (BC), black carbon refractive index measurements are difficult. There are substantial differences among the over 40 existing measurement schemes and no two schemes are the same. Three typical BC refractive index schemes are chosen to explore the difference in black carbon optical properties and the consequences of the radiative effect. Two schemes are widely used in climate models, and the third is from a newer measurement in 2016. It is shown that black carbon optical properties are sensitive to different refractive indices. The relative differences in extinction coefficient and single scattering albedo can be over 100%. In addition, by using Maxwell–Garnett and Bruggeman mixing rules, it has been found that the effect of internal mixing on aerosol optical properties depends strongly on the choice of refractive index. Using a one‐dimensional radiative transfer model under clear‐sky conditions, we demonstrate that the choice of black carbon refractive index influences the inferred radiative effect. Using the more recent (2016) scheme for pure black carbon can increase the top‐of‐atmosphere radiative effect by 20% relative to the currently widely used lowest‐absorbing scheme. For internally mixed aerosol, the sign of the radiative effect can change depending on which refractive index is used.

The use of a genetic algorithm in optical thin film design and optimisation

We used a genetic algorithm in the design and optimisation of optical thin films and present the effects of the choice of variables, refractive index and optical thickness, in both applications of this algorithm, in this paper. The Fourier transform optical thin film design method was used to create a starting population, which was later optimised by the genetic algorithm. In the genetic algorithm design application, the effect of the choice of variable was not distinct, as it depended on the type of design specification. In the genetic algorithm optimisation application, the choice of refractive index as a variable showed a better performance than that of optical thickness. The results of this study indicate that a genetic algorithm is more effective in the design application than in the optimisation application of optical thin film synthesis.

Engineering optical soliton bistability in colloidal media

We consider a mixture consisting of two species of spherical nanoparticles dispersed in a liquid medium. We show that with an appropriate choice of refractive indices and particle diameters, it is possible to observe the phenomenon of optical soliton bistability in two spatial dimensions in a broad beam power range. Previously, this possibility was ruled out in the case of a single-species colloid. As a particular example, we consider the system of hydrophilic silica particles and gas bubbles generated in the process of electrolysis in water. The interaction of two soliton beams can lead to switching of the lower branch solitons to the upper branch, and the interaction of solitons from different branches is phase independent and always repulsive.

Potential of quarterwave interference stacks for colored thermal solar collectors

The architectural integration of thermal solar collectors into buildings is often limited by their black color and the visibility of tubes and corrugations of the absorber sheets. A certain freedom in color choice would be desirable, but the colored appearance should not cause excessive energy losses. Multilayered interference filters on the collector glazing can produce a colored reflection, hiding the corrugated metal sheet, while transmitting the non-reflected radiation entirely to the absorber. We investigate the potential of quarterwave stacks by simulation of their optical behavior, yielding the visible reflectance R VIS, the solar transmittance T sol, a figure of merit M = R VIS/ R sol, and the CIE color coordinates. The necessary number of individual layers in the multilayer stack as well as the choice of refractive indices and thus of thin film materials are discussed. Finally, examples for realistic multilayer designs are proposed.

Radiative properties and direct effect of Saharan dust measured by the C‐130 aircraft during Saharan Dust Experiment (SHADE): 2. Terrestrial spectrum

In situ measurements of terrestrial radiation from the C‐130 aircraft during the Saharan Dust Experiment (SHADE) are used to quantify the effect of a strong dust outbreak on radiance and brightness temperatures. The dust gives a distinct spectral signature in upwelling and downwelling terrestrial radiation when high spectral resolution data for a dusty day is compared to data from a clear day. A radiative transfer model is used together with a size distribution retrieved from Sun photometers and atmospheric profiles from dropsondes to simulate the radiance data and provide a constraint on the refractive indices of Saharan dust in the terrestrial part of the spectrum. The degree of agreement between observed and simulated brightness temperatures is dominated by the choice of refractive index, the mass loading, and the altitude of the dust layer. The uncertainties in size distribution appear to have less of an effect so long as large particles (radius greater than 1 μm) are included. In the terrestrial spectrum the dust produced a relative warming rate of up to 0.5 K/day below the dust and a relative cooling of up to 0.5 K/day within the dust layer itself. The effect on irradiance due to this dust outbreak was a decrease in upwelling terrestrial radiation at the top of the atmosphere of 6.5 Wm−2 and an increase in downwelling terrestrial radiation at the surface of 11.5 Wm−2. The dust led to decreases in brightness temperature of 2–4 K in the window region, consistent with apparent features in the sea surface temperature retrieved from the advanced very high resolution radiometer.

A comparison of radiative characteristics for fly ash and coal

Numerical results for extinction efficiency, phase function, albedo and asymmetry factor are presented for clouds of spherical particles illuminated by black body radiation. the refractive indices ( m = m 1 − im 2) used were m 1 = 1.5 with m 2 varied from 0 to 0.024 in steps of 0.006 and m = 1.6 − i0.6, chosen to be representative of fly ash and coal. averaged scattering data are given for use in radiative transfer modelling of pulverised fuel furnaces. the results are seen to depend on the product of the mean particle size and the radiation temperature. the scattering parameters of fly ash are shown to vary significantly with absorption index m 2 for small particles, but the choice of refractive index is not critical for large particles.

OPTICAL GLASS FROM THE VIEWPOINT OF THE LENS DESIGNER*

AbstractThe glass used in the manufacture of lenses must be chemically stable and substantially free from bubbles, color, and striae. The lens designer is then concerned only with the refractive index and the dispersive power of the available glasses. Because practically every new lens must be achromatic, the positive elements used in it must be made from glass having a low dispersive power; the negative elements must have a relatively high dispersive power. The choice of refractive index is determined by many conflicting factors because the only “tools” available to the designer for the correction of many different aberrations are the radii of curvature of the lens surfaces, the thicknesses and air spaces, and the refractive indices of the glasses. The range of optical glasses commercially available and the reasons underlying the designer's selection of glass for different kinds of lenses are discussed.