ENHANCED 2ND-HARMONIC GENERATION IN A SILVER SPACER ISLANDS MULTILAYER SYSTEM

Second harmonic radiation from a silver island film may be enhanced by two orders of magnitude in multilayer structures in which the film is placed on top of a silver mirror, with an interlying quartz spacer layer of variable height. The dependence of the enhancement on spacer thickness is distinctly different for s and p polarization of the fundamental beam; minimum enhancement for p-polarized excitation coincides with an enhancement maximum for s polarization. The origin of this phenomenon is discussed in terms of stratified medium theory: It arises from an amplification of the field in the island film layer, as a consequence of coherent superposition of the multiply reflected partial waves. The excitation of localized surface plasmons in the island film is taken into account in terms of an effective dielectric constant. In agreement with symmetry arguments, the produced second harmonic radiation is predominantly p-polarized, even for s-polarized excitation. Good agreement between the model calculations and the experimentally observed thickness dependence is achieved when this tensorial character of the SHG process is taken into account.