zero path difference 

https://doi.org/10.1351/goldbook.08305
In a Michelson interferometer or other two-beam interferometer, the position of the moving mirror at which the optical paths are equal.
Source:
PAC, 2021, 93, 647. (Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)) on page 679 [Terms] [Paper]
Citation: 'zero path difference' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.08305 RIS BibTex EndNote
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