DifferentialInterferenzkontrast

DifferentialInterferenzKontrast (DIC), also called Nomarski interference contrast, is a light microscopy technique developed by Georges Nomarski in 1952 that enhances contrast in unstained, transparent specimens by converting phase shifts of transmitted light into intensity variations.

Its principle relies on a pair of nearly identical beams that traverse the specimen along slightly different, sheared paths; the optical path differences convert to phase differences, which are converted into intensity differences upon interference after recombination. The resulting image encodes the gradient of optical path length, yielding a pseudo three-dimensional relief shading that emphasizes edges and fine structures.

Optical setup includes polarized illumination, a Wollaston or Nomarski prism to split and recombine beams, and an analyzer to produce interference. The shearing direction, prism orientation, and illumination angle determine the image contrast and directionality. DIC systems are integrated into specialized microscopes and require precise alignment.

Interpretation and limitations: DIC images are rich in contrast for transparent specimens and are especially sensitive to edges; however, the image is not a direct map of thickness or refractive index and is orientation-dependent. The technique can introduce artificial shading if the sample is thick or very inhomogeneous, and it is less effective for opaque samples.

Applications: common in biology for live-cell imaging, microbiology, embryo development, tissue sections, and in materials science for inspecting microstructures. It provides high-contrast, label-free imaging compatible with routine fluorescence or phase-contrast methods.