{"term":{"id":"07458","title":"photon echo","longtitle":"IUPAC Gold Book - photon echo","doi":"10.1351\/goldbook.PT07458","code":"PT07458","status":"current","definitions":[{"id":1,"text":"Time-resolved optical spectroscopy in which the inhomogeneous broadening of absorbers is eliminated by the proper choice of geometry in a four-wave mixing experiment.","notes":{"1":"Term applied to a group of non-linear optical techniques such as integrated echo, time-gated echo, three-pulse echo peak shift, heterodyne-detected echo and 2D-echo.","2":"Photon echo techniques make use of the third-order optical polarization and 'hyper-susceptibility'. The main distinguishing feature of photon echo methods from all other third-order processes is the time ordering of the field interactions that leads to a rephasing process in the induced polarization to remove inhomogeneous contributions to the absorption linewidth.","3":"In terms of mathematical description, the photon echo is equal to the spin echo (solid-state physics) from which a term 'echo' was borrowed.","4":"Technique used, e.g., to probe solvation dynamics upon (ultra-short) pulse excitation of a chromophore."},"links":[{"term":"chromophore","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/C01076"},{"term":"non-linear optical techniques","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/NT07426"},{"term":"optical spectroscopy","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/O04314"},{"term":"polarization","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/P04712"},{"term":"solvation","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/S05747"}],"sources":["PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 394 (https:\/\/doi.org\/10.1351\/pac200779030293)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/PT07458\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/PT07458\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/PT07458\/plain"},"citation":"Citation: 'photon echo' 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.PT07458","license":"The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/) for individual terms.","collection":"If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .","disclaimer":"The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.","accessed":"2026-05-18T06:32:59+00:00"}}