Modeling Wavelength Dependent Mid-infrared (5.5–25 μm) Optical Constants of Silicate Glasses: A Genetic Algorithm Approach

Journal Article · 11 September 2023 · Earth and Space Science

DOI: https://doi.org/10.1029/2023ea002938 · OSTI ID:2281518

Varatharajan, I.  ^[1]; Sklute, E.  ^[2]; Glotch, T. D.  ^[1]; Dyar, M. D.  ^[3]

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1. Stony Brook University, NY (United States)
2. Planetary Science Institute, Tucson, AZ (United States); Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
3. Planetary Science Institute, Tucson, AZ (United States); Mount Holyoke College, South Hadley, MA (United States)

Wavelength-dependent mid-infrared (400–1,800 cm^-1; 5.56–25 μm) optical constants (real and imaginary indices of refraction; n and k) are determined using reflectance spectra at a spectral sampling of 4 cm^-1 for several silicate glasses of varying SiO₂ wt% which include (a) basaltic volcanic glass from Kilauea, Hawaii, (b) synthetic andesite, (c) two synthetic dacites, (d) obsidian volcanic glass from Mount Lassen, California, (e) synthetic rhyodacite, and (f) rhyolitic volcanic glass from Mexico. Because glasses are optically isotropic, no specific orientation was required for spectral measurements, and polished glass samples were measured at random orientations using micro-FTIR spectrometer. Lorentz-Lorenz dispersion theory and Fresnel reflectance model for high symmetry materials were used to model the optical constants by optimizing oscillator parameters in modeled spectra to match laboratory spectra. A genetic algorithm (GA) approach automatically finds the natural oscillators and their parameters for each spectrum, and then uses these parameters in a non-linear least squares optimization routine. The study compared spectral parameters such as Christiansen feature, reststrahlen bands (RBs), and the peaks centered around 860–1,100 (peak 1) and 400–480 cm^-1 (peak 2) of n and k to their respective SiO₂ wt% of the glasses. CF, RBs, peak 1 of n and k, and peak 2 of n shift to higher wavenumbers with increased SiO₂ wt%, whereas peak 2 of k shifts to lower wavenumbers with increased SiO₂ wt%. Derived optical constants of these glasses will improve quantitative abundance mapping of volcanic materials on the surfaces of silicate targets in the Solar System.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE Office of Science (SC); National Aeronautics and Space Administration (NASA)
• Grant/Contract Number: 89233218CNA000001
• OSTI ID: 2281518
• Report Number(s): LA-UR--23-29921
• Journal Information: Earth and Space Science, Journal Name: Earth and Space Science Journal Issue: 9 Vol. 10; ISSN 2333-5084
• Publisher: American Geophysical Union (AGU)Copyright Statement
• Country of Publication: United States
• Language: English