Quantitative Interference Microscopy

In any microscope, the formation of an image depends on the interference of light: according to Abbe’s theory, the image results from the interference of direct and diffracted light in the image plane. Most modern microscopes used in cell biology incorporate devices that exploit interference in the image plane for revealing phase differences introduced by transparent specimens in order to improve image contrast. Thus, it is difficult to define exactly what constitutes an interference microscope. This need not concern us here, however, because the term ‘quantitative interference microscopy’, more concisely known as ‘interferometric microscopy’, applies only to those instruments that are capable of measuring the phase difference introduced by the specimen. For example, the currently popular differential interference contrast (DIC) microscope developed by Nomarski in 1955 will not be discussed in detail here, because this is essentially an image-contrasting instrument which is not designed for measuring phase differences. Interferometric microscopes are distinct from polarizing microscopes (the only other type of microscope capable of measuring phase differences) in that they can measure phase differences introduced by optically isotropic specimens.