A Survey of Optical Constants in the 5 - 25 Micron Spectral Region.
Final rept. 3 Sep 79-2 Sep 80,
ARIZONA UNIV TUCSON DEPT OF PHYSICS
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A technique has been developed for determining the spectrum of optical constants in the vicinity of strong lattice absorption bands in the infrared region for solids available only in small particle form. The technique involves segregating a sub-micrometer size fraction of the sample for dispersal in infrared-transparent KBr pellets, measuring the transmission spectrum and fitting it with a combination of the Lorentz oscillator equations and small particle extinction theory, normally based on a random distribution of Rayleigh ellipsoids. The assumption that bulk optical constants apply to particles as small as 0.1 micrometer is supported by careful new measurements on two small particle systems where the shapes are known to be cubes MgO smoke and spheres amorphous quartz smoke. Several tests of the extinction theory for irregular shapes are discussed in cases where optical constants are well known. The method for determining optical constants has been applied to the natural silicate samples obsidian volcanic glass, serpentine, chlorite, montmorillonite, talc, and volcanic dust from the Mt. St. Helens eruption as well as to amorphous aluminum oxide smoke. The method should be most reliable for single component, isotropic solids existing in a wide distribution of particle shapes. Particular caution is expressed in application to heterogeneous materials such as soil samples and atmospheric dust samples. Author
- Atmospheric Physics
- Atomic and Molecular Physics and Spectroscopy