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A More Efficient Method for Synthetic Textile Fiber Analysis Using Polarized Light Microscopy
Author(s) -
Reffner John A.,
Kammrath Brooke W.,
Kaplan Samuel
Publication year - 2020
Publication title -
journal of forensic sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.715
H-Index - 96
eISSN - 1556-4029
pISSN - 0022-1198
DOI - 10.1111/1556-4029.14252
Subject(s) - optics , fiber , materials science , refractive index , polarized light microscopy , graded index fiber , optical fiber , anisotropy , step index profile , microscopy , refractive index profile , polarization maintaining optical fiber , fiber optic sensor , optoelectronics , physics , composite material
The efficiency of conventional polarized light microscopy (PLM) methods for analyzing synthetic fiber evidence analyses is improved. Historically, using PLM for fiber identification relied on measuring refractive index. This prior PLM technology is reliable, but it is not efficient. Most fibers are optically anisotropic, having two principal refractive index values, N (High) and N (Low) . When the fiber is mounted in intermediate refractive index medium, efficiency is improved by observing the change in contrast while the polarized light’s vector is rotated relative to the fiber’s axis. Minimum contrast occurs when the refractive indices of the mounting medium and fiber are equal. This angle of equality is determined by orienting the fiber’s highest refractive index parallel to the polarized light’s electric field vector, rotating the fiber or polarizing element, observing minimum contrast and measuring the angle of equality. This method is rapid, reduces remounting fibers in different mounting media and provides a quantitative measure for fiber comparisons.