Optical second harmonic generation from thin silver films

In this work, silver films of various thicknesses from 1 to 180 nm are vacuum evaporated on microscopic glass plates. The external reflection (ER) measurement of the second-harmonic generation (SHG) indicates that the peak intensity decreases dramatically as the film thickness is reduced below 20 nm and the incident angle yielding maximum SHG shifts toward lower values. The theoretical calculation based on the hydrodynamical model with excitation and interference of multiple reflections on both surfaces of the metal film can successfully address the salient features of these observations. Enhancement of the SHG light occurs only for film thickness as small as 15 nm, where the granular structure is obvious as observed from an atomic force microscope. (C) 1997 Elsevier Science B.V.