Plasmon-Enhanced Second-Harmonic Generation from Ionic Self-Assembled Multilayer Films

We have demonstrated large enhancements of the effective second-order nonlinear susceptibility (ł(2)) of ionic self-assembled multilayer (ISAM) films, causing a film with just 3 bilayers to be optically equivalent to a 700−1000 bilayer film. This was accomplished by using nanosphere lithography to deposit silver nanoparticles on the ISAM film, tuning the geometry of the particles to make their plasmonic resonances overlap the frequency of optical excitation. An enhancement in the efficiency of second harmonic generation (SHG) by as much as 1600 times was observed. Even though this is already a large value, we suggest that further refinements of the techniques are expected to lead to additional enhancements of similar or larger magnitude. Second-order nonlinear optical (NLO) materials are at the heart of telecommunications devices such as electro-optic modulators and optical switches, and in lasers such as high-power green and blue solid-state lasers and optical parametric amplifiers. Conventional NLO materials generally consist of inorganic crystals such as KTP, LiTaO3, and LiNbO3.1 While they are quite efficient, high-quality crystals of sufficient size ar