Abstract

Second harmonic generation at surfaces (SSHG) has recently been the subject of increasing interest among researchers who require a probe of interfacial phenomena that is both surface-specific and can be utilized in condensed phase studies (see [1] and references therein). SSHG belongs to a larger class of second order nonlinear optical processes that includes optical rectification, sum and difference frequency mixing, and the Pockles effect, all of which are symmetry forbidden in isotropic media (at least in the electric dipole approximation [1]). At an interface between dissimilar media the isotropy which may be present in the bulk material is disturbed, and processes such as second harmonic generation can occur. This property is attractive for probing surface phenomena because only very weak electric quadrupole and magnetic dipole signals are generated in the bulk material. Furthermore, SSHG is an optical effect and requires only transparency of the media at the fundamental and harmonic wavelength, rather than the more stringent condition of ultrahigh vacuum imposed by electron and ion probes.

© 1985 Optical Society of America