Differential Interference Contrast (DIC), also known as Nomarski Contrast, helps to visualize small height differences on the specimen surface, thus enhancing feature contrast.

DIC uses a Wollaston prism together with a polarizer and analyzer whose transmission axes are perpendicular (crossed at 90°) to each other. The two light waves split by the prism are made to interfere after reflection from the specimen surface, rendering height differences visible as variations in color and texture.

For the majority of cases, incident light microscopy provides most of the required information, but for some cases, in particular polymers and composite materials, transmitted light microscopy (for transparent materials) and the use of stains or dyes can provide insights into the microstructure that would remain hidden when using standard bulk sample preparation and normal incident illumination.

Because many thermoset materials are inert to common metallographic etchants, the sample’s microstructure is often best observed with transmitted polarized light to enhance the differences in refractive index of discrete features.

Differential Interference Contrast (DIC): DIC visualizes height and phase differences. A Wollaston prism splits polarized light into an ordinary and an extraordinary wave. These waves vibrate at right angles to each other, propagate at different rates and are physically separate. This results in a 3D image of the sample surface, although no real topographical information can be derived from it.