Fizeau fringes are interference fringes observed in an interferometer, specifically in a Fizeau interferometer. The Fizeau interferometer is named after the French physicist Armand Fizeau, who developed it in the mid-19th century. It is commonly used for testing optical surfaces, such as lenses and mirrors.
The interference fringes observed in a Fizeau interferometer result from the interference of light waves that have traveled different paths. Here is a brief explanation of how Fizeau fringes are generated:
Setup: In a Fizeau interferometer, a beam of light is split into two parts. One part is directed towards a reference mirror, and the other part is directed toward the surface under test (e.g., a lens or mirror). Both beams are then reflected back and recombine.
Interference: The two beams, having traveled different paths, recombine and interfere with each other. Depending on the optical path difference between the reference beam and the test beam, interference patterns are formed.
Fringe patterns: Fizeau fringes manifest as alternating bright and dark bands or fringes in the interferometer's field of view. These fringes represent constructive and destructive interference of the light waves.
Surface testing: By observing the Fizeau fringes, one can analyze the optical surface under test. Changes in the surface profile or imperfections alter the optical path length, leading to changes in the interference pattern.
Fizeau interferometers are widely used for testing the flatness and quality of optical surfaces in various industries, including optics manufacturing and astronomy. The analysis of Fizeau fringes allows for precise measurements and assessments of the surfaces being tested.