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Differential interference contrast microscopy
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<p>Differential interference contrast (DIC) microscopy, also known as Nomarski interference contrast (NIC) or Nomarski microscopy, is an <a href="/facts/Optical_microscopy/5700vcna">optical microscopy</a> technique used to enhance the <a href="/facts/Contrast_(vision)/zD9F91Je">contrast</a> in unstained, transparent <a href="/facts/Sample_(material)/lh2pPYky">samples</a>. DIC works on the principle of <a href="/facts/Interferometry/X3E1SsQT">interferometry</a> to gain information about the <a href="/facts/Optical_path_length/qpXIMzqz">optical path length</a> of the sample, to see otherwise invisible features. A relatively complex optical system produces an image with the object appearing black to white on a grey background. This image is similar to that obtained by <a href="/facts/Phase_contrast_microscopy/BmUkx69q">phase contrast microscopy</a> but without the bright diffraction halo. The technique was invented by Francis Hughes Smith. The "Smith DIK" was produced by Ernst Leitz Wetzlar in Germany and was difficult to manufacture. DIC was then developed further by Polish physicist <a href="/facts/Georges_Nomarski/fDIy5XuV">Georges Nomarski</a> in 1952. </p><p>DIC works by separating a <a href="/facts/Polarization_(waves)/fP33m0eD">polarized</a> light source into two <a href="/facts/Orthogonality/JVIjYPog">orthogonally</a> polarized mutually coherent parts which are spatially displaced (sheared) at the sample plane, and recombined before observation. The interference of the two parts at recombination is sensitive to their optical path difference (i.e. the product of <a href="/facts/Refractive_index/yjkzvgeE">refractive index</a> and geometric path length). Adding an adjustable offset phase determining the interference at zero optical path difference in the sample, the contrast is proportional to the path length gradient along the shear direction, giving the appearance of a three-dimensional physical relief corresponding to the variation of optical density of the sample, emphasising lines and edges though not providing a topographically accurate image. </p>