The Jamin interferometer is a type of

interferometer Interferometry is a technique which uses the '' interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber o ...

, related to the

Mach–Zehnder interferometer The Mach–Zehnder interferometer is a device used to determine the relative phase shift variations between two collimated beams derived by splitting light from a single source. The interferometer has been used, among other things, to measure pha ...

. It was developed in 1856 by the French physicist

Jules Jamin Jules Célestin Jamin (31 May 1818, Termes, Ardennes – 12 February 1886) was a French physicist. He was professor of physics at École Polytechnique from 1852 to 1881 and received the Rumford Medal in 1858 for his work on light. He improved Br ...

. The interferometer consists of two

mirror A mirror or looking glass is an object that Reflection (physics), reflects an image. Light that bounces off a mirror will show an image of whatever is in front of it, when focused through the lens of the eye or a camera. Mirrors reverse the ...

s, made of the thickest glass possible. The

Fresnel reflection The Fresnel equations (or Fresnel coefficients) describe the reflection and transmission of light (or electromagnetic radiation in general) when incident on an interface between different optical media. They were deduced by Augustin-Jean Fresne ...

from the first surface of the mirror acts as a

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 wid ...

. The incident light is split into two rays, parallel to each other and displaced by an amount depending on the thickness of the mirror. The rays are recombined at the second mirror and ultimately imaged onto a screen. If a phase-shifting element is added to one arm of the interferometer, then the displacement it causes can be determined by simply counting the interference fringes, i.e., the minima. The Jamin interferometer allows very exact measurements of the

refractive index 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, o ...

and

dispersion Dispersion may refer to: Economics and finance * Dispersion (finance), a measure for the statistical distribution of portfolio returns *Price dispersion, a variation in prices across sellers of the same item * Wage dispersion, the amount of variat ...

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

es; a transparent pressure chamber can be positioned in the instrument. The

phase shift In physics and mathematics, the phase of a periodic function F of some real variable t (such as time) is an angle-like quantity representing the fraction of the cycle covered up to t. It is denoted \phi(t) and expressed in such a scale that it ...

due to changes in pressure is quite easy to measure.

References

* * * Figures 1 and 2 at p. 513. Interferometers {{optics-stub