NONLINEAR OPTICS FROM SURFACES AND INTERFACES

Optical second harmonic generation and sum frequency generation have r ecently been established as versatile techniques for the study of stru ctural and electronic properties of a wide variety of surfaces and int erfaces. Several examples will be discussed which illustrate the.capab ility of these techniques of providing relevant information that is no t easily accessible via traditional optical or electronic spectroscopi es. Also, an overview of the recent theoretical progress will be given which has led to a microscopic understanding of the nonlinear optical signal for several systems.