Giant Raman scattering and second harmonic generation on a surface

A study is made of the generation of a giant second harmonic and of the giant Raman scattering of light on a surface separating a solid from an electrolyte. The intensity of the giant second harmonic is shown to depend on the electrolyte composition, nature of the solvent, and presence of additives in the form of organic compounds. An electric field in a double layer may alter the nonlinear optical susceptibilities of the components of the double layer. Generation of a giant second harmonic may provide a convenient method for telemonitoring of the surfaces of metals and semiconductors (for example, for the determination of the zero charge potential) in technological processes. The gain of the second harmonic generation process is (3–5)×10⁴, which is of the same order as the gain of the giant Raman scattering, (5–10)×10⁴, which depends reversibly on the electrode potential φ, suggesting a common mechanism of these phenomena: an increase in the local field near projections of the surface of a metal.