Nomarski differential phase contrast

Nomarski differential interference contrast microscopy is an alternative to phase contrast microscopy which gives an almost three... 

The Nomarski differential interference contrast technique accentuates changes in specimen thickness and refractive index in transmission without giving the haloes round fine features that distract from the usefulness of the phase-contrast technique. In reflection, images are obtained that strongly accentuate the topographical features present. 

Nomarski microscopy is an examination mode using differential interference contrast (DIC). The images that DIC produces are deceptively three-dimensional with apparent shadows and a relief-like appearance. Nomarski microscopy also uses polarized light with the polarizer and the analyzer arranged as in the polarized light mode. In addition, double quartz prisms ( Wollaston prisms or DIC prisms) are used to split polarized light and generate a phase difference. 

Another system for examination of low-contrast objects such as living cells is the Nomarski or differential interference contrast system. It is also particularly useful for materials that cannot be stained satisfactorily for other reasons, such as very thin sections that take up too little stain. This system employs polarizing filters and quartz prisms instead of the annular diaphragm and phase plates used in phase contrast. This eliminates the halo effect seen in phase contrast, rendering sharply defined images with good contrast, having a characteristically (pseudo) three-dimensional appearance. It is rather less suited to routine work than phase contrast however, and is considerably more expensive. 

Patches are normally obtained under an inverted microscope. The magnification will depend on the size of the cells that are going to be studied. Illumination is phase contrast or differential interference contrast (Nomarski) in order to have a clear image of cells, taking into account that they are living cells without any dye. The illumination power supply of the microscope has to be localized far from the set-up, especially when it is an a.c. power supply. 

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