A Mirau interferometer works on the same basic principle as a

Michelson interferometer The Michelson interferometer is a common configuration for optical interferometry and was invented by the 19/20th-century American physicist Albert Abraham Michelson. Using a beam splitter, a light source is split into two arms. Each of those li ...

. 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 In optical engineering, the objective is the optical element that gathers light from the object being observed and focuses the light rays to produce a real image. Objectives can be a single lens or mirror, or combinations of several optical elem ...

assembly. It is named after André Henri Mirau, who filed a patent on the concept in 1949. atent US2612074 https://patents.google.com/patent/US2612074/ref> A schematic of a Mirau interferometer is shown on the right. At the

beam splitter A beam splitter or ''beamsplitter'' is an optical device that splits a beam of light into a transmitted and a reflected beam. It is a crucial part of many optical experimental and measurement systems, such as interferometers, also finding wide ...

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.

Immersion Mirau Interferometer

An immersion Mirau interferometer is a modification of a Mirau interferometer, in which the light path is immersed in a liquid medium. One application of an immersion Mirau interferometer is to image cells with

medium Medium may refer to: Science and technology Aviation *Medium bomber, a class of war plane *Tecma Medium, a French hang glider design Communication * Media (communication), tools used to store and deliver information or data * Medium of ...

. Since the

index of refraction In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

of the medium is substantially different from that of the neighboring air, each millimeter of medium would introduce a path length difference from the reference wave, and ideal interference conditions are lost. Filling the microscope optics with medium restores the ideal interference conditions.

Simultaneous Immersion Mirau Interferometer

In immersion Mirau interferometry, the interference patterns needed to reproduce the image are acquired at different times and vibrations, if they exist, prevent maintaining the desirable phase shifts between consecutive frames. Thus immersion Mirau interferometry is very sensitive to vibrations. One solution is to acquire all interference images at the same time. This is known as a simultaneous immersion Mirau interferometer.

References

{{reflist Interferometers

Immersion Mirau Interferometer

Simultaneous Immersion Mirau Interferometer

See also

References