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The accuracy of refractive and absorptive indices derived from reflectance measurements on low‐reflecting materials
Author(s) -
Cook A. C.,
Murchison D. G.
Publication year - 1977
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1111/j.1365-2818.1977.tb01114.x
Subject(s) - refractive index , reflectivity , wavelength , optics , absorption (acoustics) , refraction , materials science , chemistry , physics
SUMMARY Errors in the refractive and absorptive indices derived from reflectance measurements on relatively low‐absorbing organic substances in two media are discussed, with particular reference to coal macerals and cokes. Variation of errors in refractive and absorptive indices at different levels of reflectance, and the effect of different combinations of sign and magnitude of reflectance error on the two parameters, are presented in both tabulated form and as diagrams. The errors in the refractive and absorptive indices vary in relation to reflectance level, the reflectance difference between standard and unknown, the difference between the refractive indices of the unknown and the immersion oil and the wavelength of reflectance measurement within the visible spectrum. Despite the variation, it is possible to obtain useful values for the parameters within the low‐absorbing range. If the absorption is negligible, it may not be possible to obtain realistic values for absorptive index, but even where this is the case, satisfactory values for refractive index can still be obtained. Suggestions are made on how to minimize reflectance errors and to increase the accuracy of dispersion curves for derived refractive and absorptive indices within the visible spectrum.