Abstract
A hyperspectral imaging instrument analyzing fibers between crossed polarizers
spectrometrically is presented. The principle of operation is introduced and
illustrated briefly by the theory of polarization and birefingence and calculations
based on Stokes parameters and Müller matrices. Afterward, the developed
instrumentation and results are detailed. Results obtained by the calculations and
developed instrumentation indicate that the retardance of birefringent materials can
be calculated over a high range and with a high accuracy. In addition, the spatial
resolution of the instrument suffices to analyze different regions within a fiber
individually. This allows the selection of a region at the center of an analyzed
fiber that is shown to provide an optimal signal. The developed software enables
analysis of the polarization color and the “normal”, i.e., absorptive color of the
sample individually. These features make possible a preliminary identification of
fibers, without isolation of the fiber from a microscope slide. The instrument forms
a powerful new approach to automated analyses in forensic fiber evidence, as it can
establish analyses of morphology, color, and identity of a set of samples in a
high-throughput, automated, and objective way.
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