What Is a DIC Microscope?
A differential interference contrast (DIC) microscope, also known as a Nomarski microscope, is an optical microscope designed for viewing colorless and transparent specimens. It was pioneered by Georges Nomarski in 1954, utilizing a special prism known as the Nomarski prism to enhance image contrast without staining the specimen.
Uses of DIC Microscopes
DIC microscopes are invaluable in observing biological materials such as cells, where traditional optical microscopes fall short due to the transparency of such specimens. This technique enables detailed examination of live cells and their internal structures without the need for dyes or stains, preserving the specimen’s integrity.
Principle of DIC Microscopes
The DIC microscope operates by converting natural light from the source into linearly polarized light through a polarizer. This light, upon passing through a Wollaston prism, divides into two beams with orthogonal polarization. These beams traverse the specimen, accumulate phase differences, and recombine in a second Wollaston prism. The recombined light, now exhibiting interference patterns, undergoes polarization in the same direction before reaching the observer, rendering transparent specimens visible in three dimensions.
Structure of DIC Microscopes
Essentially, a DIC microscope incorporates a standard bright field microscope setup augmented with two polarizing plates and two Nomarski prisms. This arrangement allows for versatile use; removing the Nomarski prisms and polarizers reverts the system to a conventional bright field or polarizing microscope, respectively. The journey of light from the source to the observer in a DIC microscope involves sequential interaction with a polarizer, Wollaston prism, specimen stage, objective lens, second Wollaston prism, analyzer, and eyepiece, facilitating the visualization of polarized light interference and the resulting optical path differences.
How to Select DIC Microscopes
DIC microscopy is particularly effective for examining unstained biological specimens, including single-celled organisms, tissue cultures, and small multicellular animals. It offers superior resolution and image clarity compared to bright-field microscopy but is less effective for specimens with minimal refractive index variation from the surrounding medium or for thicker, heavily pigmented samples. While DIC imaging can provide high-quality, artifact-free images under optimal conditions, interpretation must consider the prism’s orientation, with sample rotation often necessary to fully visualize structural details.