Term: photon echo
https://doi.org/10.1351/goldbook.PT07458

Definition:
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:
0) Term applied to a group of @NT07426@ such as integrated echo, time-gated echo, three-pulse echo peak shift, heterodyne-detected echo and 2D-echo.
1) Photon echo techniques make use of the third-order optical @P04712@ 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 @P04712@ to remove inhomogeneous contributions to the absorption linewidth.
2) In terms of mathematical description, the photon echo is equal to the spin echo (solid-state physics) from which a term 'echo' was borrowed.
3) Technique used, e.g., to probe @S05747@ dynamics upon (ultra-short) pulse excitation of a @C01076@.

Related Terms:
1) non-linear optical techniques (http://doi.org/10.1351/goldbook.NT07426).
2) polarization (http://doi.org/10.1351/goldbook.P04712).
3) solvation (http://doi.org/10.1351/goldbook.S05747).
4) chromophore (http://doi.org/10.1351/goldbook.C01076).
5) optical spectroscopy (http://doi.org/10.1351/goldbook.O04314).

Source: PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 394 (https://doi.org/10.1351/pac200779030293)

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. https://doi.org/10.1351/goldbook.PT07458

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