Doubly-resonant sum-frequency generation spectroscopy for surface studies

Doubly-resonant infrared–visible sum-frequency generation (DR-SFG) as a two-dimensional surface spectroscopy was demonstrated experimentally for the first time. Probing electronic and vibrational transitions of a surface molecular monolayer simultaneously, the technique gives access to information about the electron-vibration coupling of the surface molecules. It allows selective studies of any interface accessible by light.