Interferometry

Interferometry is a family of measurement techniques that compares waves by combining them and analyzing their interference. The resulting patterns reveal quantities such as distance, wavelength, refractive index, or surface shape.

Optical path length: The product of a light path’s geometric length and the refractive index along it. Interferometers respond to differences in optical path length between waves.
Optical metrology: The use of light-based instruments and standards to measure physical quantities. Interferometry is a core method for high-precision dimensional measurement.
Thomas Young: An English physician and physicist whose work established evidence for the wave nature of light. His double-slit experiment made interference a defining test of wave behavior.
Spectroscopy: The study of how matter interacts with electromagnetic radiation as a function of wavelength or frequency. Spectroscopy often measures spectral intensity, whereas interferometry extracts information from phase relationships.
Phase (waves): The position of a point in a wave cycle, usually expressed as an angle or fraction of a cycle. A path-length difference changes relative phase and therefore the observed interference.
White-light interferometry: An interferometric method that uses broadband light to measure surface height from localized fringe visibility. Its short coherence length helps locate surface features without fringe-order ambiguity.
Young's double-slit experiment: An experiment in which light passing through two slits forms an interference pattern on a screen. It demonstrated the pattern-making principle later harnessed for measurement.
Triangulation: A method for determining position by measuring angles from known locations. It infers distance geometrically rather than from interference phase.
Interference (wave propagation): The superposition of waves that produces reinforcement or cancellation according to their relative phase. Interferometry turns this general wave phenomenon into a measurement method.
Laser Doppler vibrometry: A non-contact technique that measures surface vibration from the Doppler shift of reflected laser light. Interferometric phase changes reveal minute motion and vibration.

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