In physics, coherence theory is the study of optical effects arising from partially coherent light and radio sources. Partially coherent sources are sources where the coherence time or coherence length are limited by bandwidth, by thermal noise, or by other effect. Many aspects of modern coherence theory are studied in quantum optics.

The theory of partial coherence was awoken in the 1930s due to work by Pieter Hendrik van Cittert and Frits Zernike.

Topics in coherence theory

• Interferometric visibility – which quantifies interference contrast in opticsPages displaying wikidata descriptions as a fallback
• Mutual coherence function
• Degree of coherence
• Van Cittert–Zernike theorem
• Michelson stellar interferometer – Type of array used for astronomical observations
• Correlation interferometry – Astronomy devicePages displaying short descriptions of redirect targets
• Hanbury–Brown and Twiss effect – Quantum correlations related to wave-particle dualityPages displaying short descriptions of redirect targets
• Phase-contrast microscope – Optical microscopy techniquePages displaying short descriptions of redirect targets
• Englert–Greenberger duality relation – A relation of quantum opticsPages displaying short descriptions of redirect targets