Michelson interferometer

An optical instrument that splits a beam into two paths, reflects them back, and recombines them to produce interference. Changes in the resulting pattern reveal differences in optical path length or phase.

Beam splitter: An optical component that divides an incident beam into transmitted and reflected parts. It sends light into the interferometer’s two arms and recombines returning beams.
Michelson–Morley experiment: A 1887 experiment that used an interferometer to test for Earth’s motion through the proposed luminiferous ether. It used fringe comparisons as Earth’s orientation changed to seek an ether-wind signal.
Albert A. Michelson: An American physicist known for precision optical measurements and the speed-of-light experiments bearing his name. He developed the instrument and used it in increasingly precise optical experiments.
Wave optics: The description of light as waves, including diffraction, interference, and polarization. The instrument’s fringes follow directly from wave superposition.
Optical path length: The product of a light path’s geometric length and the refractive index along it. The instrument compares optical path lengths, not distance alone.
Michelson stellar interferometer: An interferometer that uses separated apertures to measure angular sizes of stars. Michelson adapted interference to estimate stellar diameters from fringe visibility.
Edward Morley: An American chemist and physicist who collaborated with Michelson on the 1887 ether-drift experiment. His collaboration produced the best-known early application of the interferometer.
Optical cavity: A structure that confines light between reflective boundaries, often producing repeated resonances. Unlike a cavity, the basic Michelson arrangement compares two returning paths rather than storing light through repeated reflections.
Interference: The superposition of waves that produces reinforcement or cancellation according to their relative phases. Interference converts the arms’ phase difference into observable intensity variation.
Fourier-transform spectroscopy: A spectroscopic method that derives a spectrum from measurements of an optical signal over varying path difference. A Michelson interferometer scans path difference to encode a source’s spectrum.

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