Surface nonlinear optics: a historical overview

A comprehensive theory of the behavior of light waves at the boundary of nonlinear optical media was first presented in 1962. Observation of second harmonic reflected light quickly followed, first from media which lack inversion symmetry, but soon thereafter from silver, silicon, germanium, and ionic crystals. While it was established in the mid-sixties that second harmonic and sum frequency generation could be used to investigate specifically the structures of surfaces and interfaces of centrosymmetric materials, it was not until about 1980 that nonlinear optical spectroscopy of surfaces became well established as a separate subfield. The availability of widely tunable dye lasers and optical parametric oscillators permit the detection of surface specific electronic and vibrational states. Polarization dependent studies yield information about the orientation of molecular monolayers and surface specific bonds. The use of picosecond and femtosecond pulse-probe techniques permits time-resolved studies of surface phase transformations, desorption, and melting. A few examples from the rapidly growing literature are selected to illustrate this historical evolution.