Practice question

Differential interference contrast creates a striking pseudo-three-dimensional relief appearance of transparent specimens. It employs plane-polarized light split by a Wollaston or Nomarski prism into two orthogonally polarized, closely spaced beams that traverse adjacent points in the sample. Different optical path lengths introduce phase gradients, and after passing through a second prism the beams recombine and interfere. Edges with steep refractive index changes appear highlighted with shadow-cast contrast. This optical sectioning reveals detailed morphology of living protists, nuclei and cytoskeletal boundaries without fluorescent labeling or staining artifacts.