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 opt ...
, 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 p ...
. It was developed in 1856 by the French physicist
Jules Jamin.
The interferometer consists of two
mirror
A mirror, also known as a looking glass, is an object that Reflection (physics), reflects an image. Light that bounces off a mirror forms an image of whatever is in front of it, which is then focused through the lens of the eye or a camera ...
s, made of the thickest glass possible. The
Fresnel reflection from the first surface of the mirror acts as a
beam splitter
A beam splitter or beamsplitter is an optical instrument, 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 Interferometry, int ...
. 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 the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...
and
dispersion of
gases; a transparent pressure chamber can be positioned in the instrument. The
phase shift
In physics and mathematics, the phase (symbol φ or ϕ) of a wave or other 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 expressed in such a s ...
due to changes in pressure is quite easy to measure.
References
*
*
* Figures 1 and 2 at p. 513.
Interferometers
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