Measurement method from non-linear optics in which a structurally-ordered sample at an interface between two phases is irradiated by single frequency visible and variable frequency infrared pulses of light to generate a sum frequency vibrational spectrum of the interfacial species without any bulk phase contribution.
Note: Closely related to second harmonic generation.
Source:
PAC, 2020, 92, 1781. 'Glossary of methods and terms used in surface chemical analysis (IUPAC Recommendations 2020)' on page 1793 (https://doi.org/10.1515/pac-2019-0404)