Light Basics
This optical instrument uses crossed polarizers and is the primary tool forensic scientists use to view trace evidence like fibers and minerals.
What is a Polarized Light Microscope (PLM)?
This everyday solid material—often found shattered at hit-and-run crime scenes—is a classic example of an isotropic substance.
What is glass?
Synthetic materials like nylon, polyester, and rayon fall into this category of trace evidence.
What are anisotropic materials?
This term describes the bending of a light wave as it passes from one medium (like air) into another medium (like glass).
What is Refractive Index?
Because light travels through isotropic materials at the same speed regardless of angle, they only have a single one of these values.
What is a single refractive index?
This phenomenon occurs when an anisotropic material splits a single incoming light beam into two distinct rays traveling at different speeds.
What is birefringence (or double refraction)?
When two polarizing filters are aligned at 90-degree angles to each other, they create this dark visual field.
What is crossed polars?
When viewed under a Polarized Light Microscope with crossed polarizers, isotropic materials will consistently appear this color.
What is dark (or black / isotropic extinction)?
Under crossed polarizers, anisotropic substances light up and display a vibrant spectrum of these distinct hues.
What are interference colors?