IN SITU PROBING OF ELECTRONIC SURFACE STRUCTURE IN IONIC CRYSTALS BY RESONANT SECOND HARMONIC GENERATION

Abstract
Resonant second harmonic generation at the surface of transparent ionic crystals is used to investigate the electronic properties of these surfaces. We report on in situ measurements on barium fluoride, sodiumchloride, and potassiumchloride in air. From the divalent crystal, the second harmonic signal should be mainly due to surface dipole interaction, since it shows spectral resonances and the dependence on azimuthal crystal orientation reflects the surface symmetry. From the monovalent crystals, the purely surface signal does practically not depend on the azimuthal crystal orientation, and should hence be due mainly to long range interaction. If one component of the light polarization is perpendicular to the surface, a surprising asymmetry is found in the signal from the alkali salts.