# Shearing interferometer

﻿
Shearing interferometer

The shearing interferometer is an extremely simple means to observe interference and to use this phenomenon to test the collimation of light beams, especially from laser sources which have a coherence length which is usually a lot longer than the thickness of the shear plate (see graphics) so that the basic condition for interference is fulfilled.

Function

The testing device consists of a high quality optical glass (like BK-7) with extremely flat optical surfaces and usually having a slight angle between them. When a plane wave is incident at an angle of 45° (which gives maximum sensitivity) it is reflected two times. The two reflections are laterally separated due to the finite thickness of the plate and by the wedge. This separation is referred to as the "shear" and has given the instrument its name. The shear can also be produced by gratings, see "External Links" below.

Parallel-sided shear plates are sometimes used but the interpretation of the interference fringes of wedged plates is relatively easy and straightforward. Those wedged shear plates produce a graded path difference between the front and back surface reflections. As a consequence, a parallel beam of light produces a linear fringe pattern within the overlap.

With a plane wavefront incident, the overlap of the two reflected beams shows interference fringes with a spacing of $d_f = frac\left\{lambda\right\}\left\{2 * n * heta\right\}$, with "$lambda$" being the wavelength of the beam, "n" being the refractive index and "$heta$" the wedge angle. The fringes are equally spaced and will be exactly perpendicular to the wedge orientation and parallel to a usually present wire cursor aligned along the beam axis in the shearing interferometer. The orientation of the fringes varies (i.e. they are tilted on the screen) when the beam is not perfectly collimated but diverging or converging. In the latter case of a noncollimated beam (thus having a curved wavefront) is incident on a wedged shear plate the path difference between the two reflected wavefronts is increased or decreased from the case of perfect collimation, depending on the sign of the curvature. The pattern is then rotated and the beam's wavefront radius of curvature "$R$" can be calculated: $R = frac\left\{s cdot d_f\right\}\left\{lambda sin gamma\right\}$, with "$s$" the shear distance, "$d_f$" the fringe distance, "$lambda$" the wavelength and "$gamma$" the angular deviation of the fringe alignment from that of perfect collimation.

ee also

* List of types of interferometers

* [http://www.optik.uni-erlangen.de/odem/index.php?lang=e&type=10&topic=shear University of Erlangen — Optical Design and Microptics]

Wikimedia Foundation. 2010.

### Look at other dictionaries:

• Spectral phase interferometry for direct electric-field reconstruction — In ultrafast optics, spectral phase interferometry for direct electric field reconstruction (SPIDER) is an ultrashort pulse measurement technique.The basicsSPIDER is an interferometric ultrashort pulse measurement technique in the frequency… …   Wikipedia

• List of types of interferometers — Field and linear interferometers = *Astronomical interferometer / Michelson stellar interferometer *Classical interference microscopy *Cyclic interferometer *Diffraction grating interferometer (white light) *Double slit interferometer *Fabry… …   Wikipedia

• Wavefront sensor — A wavefront sensor is a device for measuring the aberrations of an optical wavefront. Although an amplitude splitting interferometer such as the Michelson interferometer could be called a wavefront sensor, the term is normally applied instruments …   Wikipedia

• Fluid Science Laboratory — The Fluid Science Laboratory is a European (ESA s) science payload designed for use in Columbus built by Alenia Aeronautica Spazio and OHB System. It is a multi user facility for conducting fluid physics research in microgravity conditions. It… …   Wikipedia

• Shear — For similarly pronounced words, see sheer, Shere, or sher. Shear as a noun may refer to:*Bias (textile), in clothing design, fabric may be cut on the shear *Cosmic shear, an effect of distortion of image of distant galaxies due to deflection of… …   Wikipedia

• Astronomical seeing — Schematic diagram illustrating how optical wavefronts from a distant star may be perturbed by a layer of turbulent mixing in the atmosphere. The vertical scale of the wavefronts plotted is highly exaggerated. Astronomical seeing refers to the… …   Wikipedia

• Optical microscope — Microscope Uses Small sample observation Notable experiments Discovery of cells Inventor Hans Lippershey Zacharias Jans …   Wikipedia

• Collimated light — In the lower picture, the light has been collimated. Collimated light is light whose rays are parallel, and therefore will spread slowly as it propagates. The word is related to collinear and implies light that does not disperse with distance… …   Wikipedia

• Collimator — Example of a particle collimator A collimator is a device that narrows a beam of particles or waves. To narrow can mean either to cause the directions of motion to become more aligned in a specific direction (i.e., collimated or parallel) or to… …   Wikipedia

• Micro SPIDER — is an implementation of Spectral phase interferometry for direct electric field reconstruction (SPIDER). It has also been termed ARAIGNEE (Another Ridiculous Acronym for Interferometric Geometrically simpliﬁed Noniterative E ﬁeld Extraction). In… …   Wikipedia