Optical Second-Harmonic Generation Behavior of Films Consisting of Nanoparticles of Conjugated Ketone Derivatives

Solid films consisting of nanoparticles of salient nonlinear optical chromophores, alpha,alpha'-di(p-dimethylaminobenzylidene)cycloalkanones, were fabricated by a method based on the Langmuir-Blodgett technique. Obtained films were highly transparent and showed optical second-harmonic generation (SHG) activity even when the bulk crystal of the employed chromophore is not SHG active. We performed SHG measurements of films consisting of SHG active and inactive chromophores in various polarization geometries. As a result, SHG response from a film consisting of a SHG inactive chromophore was found to be mainly due to the surface SHG of particles in the film. On the one hand, a film consisting of a SHG active chromophore exhibited bulk SHG responses.