Mirau Interferometer

A Mirau interferometer works on the same basic principle as a Michelson interferometer. The difference between the two is in the physical location of the reference arm. The reference arm of a Mirau interferometer is located within a microscope objective assembly.

A schematic of a Mirau interferometer is shown on the right. At the beam splitter the source light is split into a reference path (reflected) and a sampling path (transmitted onto the sample). On the comparison face there is a mirrored circle in the middle. The two paths recombine to form an interference image. By changing the z position of the sample, interference images are acquired at a sequence of path (phase) differences: 0, λ/4, λ/2, and 3λ/4. These interference maps are functions of background intensity, fringe modulation, and phase. Three such images provide enough information to solve for the topographic image of a sample.

This orientation is often used in optical profilometers due to the increase in stability between the sample and reference path lengths.

Read more about Mirau Interferometer:  Immersion Mirau Interferometer, Simultaneous Immersion Mirau Interferometer, See Also