ABSTRACT
In this paper, we numerically calculate the extinction, scattering, absorption, and radar cross sections for a randomly oriented finite conducting fiber. Calculations in the long (centimeter) and short (infrared) wavelengths are presented and compared with the fixed orientation value when the incident electric field is aligned along the fiber length. The calculations presented in this paper are necessary for the parametrization of fibers to play the role of efficient obscurant and anti-radio frequency interference.
ABSTRACT
In this article, we experimentally and theoretically test the range of applicability of a patent that predicts one-way visibility through two successive parallel aerosol clouds, one scattering dominant and the other absorption dominant. A laboratory environment experiment has been designed to determine the ranges of transmissivity and contrast enhancement that might be of interest for military applications. In this study we show that transmissivities in the several percent range and lower are essential for any reasonable contrast enhancement between the two sides of the clouds.
ABSTRACT
In this erratum, a correction of a previously computed extinction spectrum of a sample of silver fibers in the infrared [Appl. Opt.48, 5095 (2009)APOPAI0003-693510.1364/AO.48.005095] is reported. The spectrum was inaccurately computed through use of an approximation relating the E-field aligned values to those of the orientationally averaged extinction efficiency. This approximation is very close for spectral points in the vicinity of the primary resonance but not necessarily for those well away from this resonance. Here, the exact theory has been used to produce the spectra.
ABSTRACT
The absorptive and scattering optical properties of heat-treated, vapor-grown, graphite microtubes consisting of nanotubes in a "stacked cone" configuration were investigated through the visible and infrared wavelengths using photoacoustic and other spectrometric techniques. However, computations of these properties involved uncertainties that were not easily resolved; the appropriate dielectric coefficients were presumed to be a combination of the published values for the distinct orientations of graphite, but the correct proportions are not evident and none of the reasonable choices produced satisfactory agreement (within the measurement limits of error). Since both of the primary components of the extinction were measured, the appropriate computational codes were employed in reverse to compute the dielectric coefficients for the graphite microtubes. Differences, primarily for the imaginary index, are most distinct for visible and near infrared wavelengths; in this wavelength region, the imaginary index falls progressively to less than half that for the computed mixture.
ABSTRACT
Mass density normalized extinction has been both measured and computed throughout the infrared for distribution of well-separated synthesized silver fibers. The computational basis is a code originally generated for use with Drudian thin fibers at millimeter wavelengths and modified for application at wavelengths that include molecular and structural (crystalline) resonances as well as thicker fibers. The computation involved convolution of fiber responses over distributions for both fiber lengths and diameters. Agreement between the measured and the computed results was found to be close.
Subject(s)
Metals/chemistry , Models, Chemical , Spectrophotometry, Infrared/methods , Computer Simulation , Infrared Rays , Light , Scattering, RadiationABSTRACT
The measurements here are used to examine agreement with a recently developed theory for long-wavelength fibrous aerosol attenuative properties (extinction and components absorption, scattering). This is intended to be the final phase of a long and systematic examination of the theory's key features. In this case the parameters are high conductivities coupled with a broad range of fiber diameters. It is clear that there is a limit on the extinction efficiency or effective extinction cross section per unit fiber volume. This limit is represented by the fiber diameter of translucency, that is, the diameter at which the fiber is not completely opaque to the electromagnetic energy. The transition is approximated by the classical skin depth of the fiber. Above this diameter the peak extinction efficiency decreases with an increase in diameter at approximately the same rate for all conductors. The scattering resonance producing this peak becomes stronger as the diameter increases. Our data confirm that for fiber diameters below the skin depth the character of the attenuation is that of absorption.
