Double refraction, also called birefringence, is the splitting of a light wave into two waves, traveling at different speeds, by an optically anisotropic
medium such as a crystal of Iceland spar (calcite), quartz, or topaz.
In the phenomenon of double refraction a ray of unpolarized light is split
into two rays plane-polarized (see polarization)
at right-angles to each other. One is refracted in the normal way, the other
with a refractive index that depends
on the original direction of the ray.
|Double refraction displayed by a crystal
of Iceland spar
AND OPTICAL PHENOMENA