Macroscopic spread function analysis for subsurface scattering in semitransparent materials
Abstract
The macroscopic spread function is a distribution of reflected flux along a surface of a semitransparent material due to the effects of surface and subsurface scattering. The spreading factor has been defined as the percentage of the reflected flux lost from the region on the surface outside the illumination diameter. The experimental results reveal that the spreading factor is least for the plastic samples when measuring an off-white sample at 700 nm and for the reagent strip formats when measuring Glucofilm$\sp{\rm TM}$ reagent strips at 800 nm. For the plastic samples, least spreading occurred with the $55\sp\circ$ reflected angle, while for the reagent strip formats, least spreading occurred with the $45\sp\circ$ reflected angle. The Monte Carlo simulations revealed that spreading is less (1) at 700 nm for both plastic samples, (2) for the off-white samples at both wavelengths, or (3) using the $45\sp\circ$ reflected angle. The simulations, in general, confirm the experimental results, and the slight differences can be attributed to incorrect simulation assumptions, such as uniform scattering distribution and Fresnel reflectance distribution. The spreading curve describes the percentage of energy reflected from the surface outside a certain field of view. Its main applications include determination of required field of view from a prescribed reflectance error tolerance, calculation of the reflectance error arising from using a certain field of view, and comparison of the spreading characteristics of two samples. An experimental setup is available for accurate measurement of the spread function. A database of spreading behavior as influenced by various geometrical and optical parameters has been compiled. A flexible Monte Carlo code has been developed to predict the spread function in semitransparent materials. The spreading curve has been defined, and has found utility in several applications of reflectometry.
Degree
Ph.D.
Advisors
DeWitt, Purdue University.
Subject Area
Mechanical engineering|Materials science
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