A More Efficient Method for Synthetic Textile Fiber Analysis Using Polarized Light Microscopy

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.