A Twyman–Green interferometer is a variant of the

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 ...

principally used to test optical components. It was introduced in 1916 by

Frank Twyman Frank Twyman (17 November 1876 – 6 March 1959) was a British designer of optical instruments and co-inventor of the Twyman–Green interferometer. Early life Twyman was born in Canterbury, Kent, England on 17 November 1876, the seventh c ...

and Arthur Green. Fig. 1 illustrates a Twyman–Green interferometer set up to test a lens. Light from a laser is expanded by a diverging lens (not shown), then is collimated into a parallel beam. A convex spherical mirror is positioned so that its center of curvature coincides with the focus of the lens being tested. The emergent beam is recorded by an imaging system for analysis. The fixed

mirror A mirror or looking glass is an object that 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 direction of the im ...

in the Michelson interferometer is rotatable in the Twyman–Green interferometer, and while the light source is usually an extended source (although it can also be a

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fi ...

) in a Michelson interferometer, the light source is always a point-like source in the Twyman–Green interferometer. The rotation of one mirror results in straight fringes appearing in the

interference pattern In physics, interference is a phenomenon in which two waves combine by adding their displacement together at every single point in space and time, to form a resultant wave of greater, lower, or the same amplitude. Constructive and destructive ...

, a fringing which is used to test the quality of optical components by observing changes in the fringe pattern when the component is placed in one arm of the interferometer.

References

Interferometers {{optics-stub