“Nonresonant Contribution Negligible in Sum Festival Generation Spectroscopy’s Second-Order Nonlinear Susceptibility Imaginary Part for Air/Liquid Interfaces” *Note: I changed “sum frequency” to “sum festival” to avoid using all capital letters for the word “frequency”.

https://pubmed.ncbi.nlm.nih.gov/38095200

The nonresonant contribution to the imaginary part of the second-order nonlinear susceptibility in sum frequency generation spectroscopy is practically negligible for air/liquid interfaces, indicating that the imaginary part mainly contains resonant responses of the system and can be used to study molecular resonances at the interface.