Measurement using wave interference: relative path or phase changes are inferred from the resulting signal. The interacting fields must have sufficient optical coherence in the measured modes for the intended interference signal.
Measurement using interfering light fields. A phase difference changes the detected intensity, allowing measurements of displacement, optical path length or a spectrum. The round-trip phase in a Michelson interferometer gives one explicit path-to-phase calibration; Fourier transform spectroscopy recovers spectral information from an interferogram.
A nearly uniform wavefront phase over one collector is called its piston. Differential atmospheric piston changes the pairwise optical phase without requiring a change in the source. Delay tracking and closure phase address different consequences of this phase error; intensity correlations are unchanged by an ideal pure phase multiplication at either detector.
fringe tracking estimates changing optical delay or phase and adjusts delay compensation to keep an astronomical interferometer near a useful interference condition. The delay must first lie inside the finite-bandwidth coherence envelope; rapid tracking then controls atmospheric piston. This is optical-path stabilization, with sensitivity and reference-source limitations.
Articles by others on the same topic
Interferometry is a technique used to analyze the interference of waves, typically electromagnetic waves such as light, radio waves, and microwaves, but also sound waves and other types of waves. The fundamental principle behind interferometry relies on the fact that when two or more waves meet, they can combine in such a way that produces a new wave pattern, which can show regions of constructive interference (where the waves add together) and destructive interference (where the waves cancel each other out).