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Proceedings Paper

Measurement of optical constants for spectral modeling: n and k values for ammonium sulfate via single-angle and ellipsometric methods
Author(s): Thomas A. Blake; Carolyn S. Brauer; Molly Rose Kelly-Gorham; Sarah D. Burton; Mary Bliss; Tanya L. Myers; Timothy J. Johnson; Thomas E. Tiwald
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Paper Abstract

The complex index of refraction, ñ = n + ik, has two components, n(ν) and k(ν), both a function of frequency, ν. The constant n is the real component, and k is the complex component, proportional to the absorption. In combination with other parameters, n and k can be used to model infrared spectra. However, obtaining reliable n/k values for solid materials is often difficult. In the past, the best results for n and k have been obtained from bulk, polished homogeneous materials free of defects; i.e. materials where the Fresnel equations are valid and there is no appreciable light scattering. Since it is often not possible to obtain such pure macroscopic samples, the alternative is to press the powder form of the material into a uniform disk. Recently, we have pressed such pellets from ammonium sulfate powder, and have measured the pellets’ n and k values via two independent methods: 1) ellipsometry, which measures the changes in amplitude and phase of light reflected from the material of interest as a function of wavelength and angle of incidence, and 2) single-angle reflectance using a specular reflectance device within a Fourier transform infrared spectrometer. This technique measures the change in amplitude of light reflected from the material of interest as a function of wavelength over a wide spectral domain. The optical constants are determined from the single-angle measurements using the Kramers-Kronig relationship, whereas an oscillator model is used to analyze the ellipsometric measurements. The n(ν) and k(ν) values determined by the two methods were compared to previous values determined from single crystal samples from which transmittance and reflectance measurements were made and converted to n(ν) and k(ν) using a simple dispersion model. [Toon et al., Journal of Geophysical Research, 81, 5733–5748, (1976)]. Comparison with the literature values shows good agreement, indicating that these are promising techniques to measure the optical constants of other materials.

Paper Details

Date Published: 5 May 2017
PDF: 9 pages
Proc. SPIE 10198, Algorithms and Technologies for Multispectral, Hyperspectral, and Ultraspectral Imagery XXIII, 101980J (5 May 2017); doi: 10.1117/12.2264501
Show Author Affiliations
Thomas A. Blake, Pacific Northwest National Lab. (United States)
Carolyn S. Brauer, Pacific Northwest National Lab. (United States)
Molly Rose Kelly-Gorham, Pacific Northwest National Lab. (United States)
Sarah D. Burton, Pacific Northwest National Lab. (United States)
Mary Bliss, Pacific Northwest National Lab. (United States)
Tanya L. Myers, Pacific Northwest National Lab. (United States)
Timothy J. Johnson, Pacific Northwest National Lab. (United States)
Thomas E. Tiwald, J.A. Woollam Co., Inc. (United States)


Published in SPIE Proceedings Vol. 10198:
Algorithms and Technologies for Multispectral, Hyperspectral, and Ultraspectral Imagery XXIII
Miguel Velez-Reyes; David W. Messinger, Editor(s)

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