Polarizing microscope

A microscope that uses controlled incident and analysed polarization of an electromagnetic wave to study specimens. Crossed polarizers reveal orientation-dependent phase retardation in a birefringent specimen.

Rotating a uniform crystallite around a fixed propagation direction changes the crossed-polar intensity factor ${\sin }^2(2\alpha )$. Extinctions repeat every90degrees and maxima occur45degrees away. Similar interference colour can coexist with different brightness if retardation is similar but azimuth differs.

An extinction pattern with four dark arms produced, for example, by a radial arrangement of local optical principal directions between crossed polarizers. The local intensity factor ${\sin }^2(2\phi )$ vanishes along the polarizer axes. Such a radial-material pattern need not be a conoscopic interference pattern.