Sum frequency generation spectroscopy

Sum frequency generation (SFG) spectroscopy is a nonlinear optical technique used to study interfaces and surfaces at the molecular level. It combines two incoming photons, typically from infrared (IR) and visible or near-infrared (NIR) laser sources, to produce a new photon whose frequency is the sum of the frequencies of the incoming photons. This process occurs primarily in non-centrosymmetric media, which is often the case at surfaces and interfaces.