Surface nonlinear optics: a historical overview

A comprehensive theory of the behavior of light waves at the boundary of no nlinear optical media was first presented in 1962. Observation of second ha rmonic reflected light quickly followed, first from media which lack invers ion symmetry, but soon thereafter from silver, silicon, germanium, and ioni c crystals. While it was established in the mid-sixties that second harmoni c and sum frequency generation could be used to investigate specifically th e structures of surfaces and interfaces of centrosymmetric materials, it wa s not until about 1980 that nonlinear optical spectroscopy of surfaces beca me well established as a separate subfield. The availability of widely tunable dye lasers and optical parametric oscill ators permit the detection of surface specific electronic and vibrational s tates. Polarization dependent studies yield information about the orientati on of molecular monolayers and surface specific bonds. The use of picosecon d and femtosecond pulse-probe techniques permits time-resolved studies of s urface phase transformations, desorption, and melting. A few examples from the rapidly growing literature are selected to illustrate this historical e volution.