Sum Frequency Generation Study on Molecular Structure of Solid Surfaces Modified with Organic Molecular Layers in Electrolyte Solutions

摘要

Sum frequency generation (SFG) spectroscopy is becoming a powerful tool in the research on surface science because of its high surface/interface selectivity. SFG is a second-order nonlinear optical process in which two photons at frequencies ω1 and ω2 generate one photon of sum-frequency at ω3=ω1 + ω2. The SFG is forbidden in the bulk of a cetrosymmetric medium and is only active at the surface or interface where the inversion symmetry is necessarily broken. For IR-visible SFG, a pulsed visible laser at a fixed frequency □1 and a pulsed infrared laser with a tunable frequency ω2 are used.