Applications of Surface Second Order Nonlinear Optical Signals

Abstract

In this chapter the theory and practice of the application of second order nonlinear optical signals to surface spectroscopy and kinetics will be described. The vast majority of nonlinear optical spectroscopic methods which were developed when high peak power pulsed lasers became available exploit the third order nonlinear susceptibility, χ ⁽³⁾. Second order nonlinear optical signals are largely of interest as a tool for frequency shifting laser output in anisotropic nonlinear crystals such as KDP (potassium dihydrogen phosphate) by second harmonic generation, optical parametric conversion, etc. The spectroscopic application of second order signals has been neglected for the very good reason that χ ⁽²⁾ is zero by symmetry in isotropic and other centrosymmetric media, which are the media of most interest in spectroscopy. However, there is one area in which this symmetry selection rule is a positive advantage, namely surface spectroscopy.