Title: free spectral range
Long Title: IUPAC Gold Book - free spectral range
DOI: 10.1351/goldbook.08607
Status: current

Definition
For a Fabry-Perot or laser cavity, wavenumber interval between successive longitudinal cavity modes of vibration; \(\Delta \tilde{\nu} = 1/(2nl)\), where \(l\) is the cavity spacing and \(n\) is the refractive index of the material in the cavity.

Note
SI unit: \(\pu{m-1}\).

Related Terms
- modes of vibration: https://goldbook.iupac.org//terms/view/08637
- wavenumber: https://goldbook.iupac.org//terms/view/08302

Source
- PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 747 (https://doi.org/10.1515/pac-2019-0203)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/08607/html
- json: https://goldbook.iupac.org/terms/view/08607/json
- xml: https://goldbook.iupac.org/terms/view/08607/xml

Citation: Citation: 'free spectral range' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.08607
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Accessed: 2026-06-07T00:07:20+00:00