Coherent interference patterns of optical second-harmonic waves from substrate-free ultrathin poly(methyi methacrylate) films asymmetrically incorporating amphiphilic dyes

An ultrathin poly(methyl methacrylate) film, as prepared by a casting-on-water method, emitted optical second harmonic (SH) light in association with asymmetric alignment of an amphiphilic dye. Coherent interference due to SH waves from a pair of films in parallel afforded a periodic pattern with the film, and the pattern was 180° phase-shifted on flipping either one of the films. These observations were ascribed to asymmetric orientation of the dye in the film and negligibly small thickness of the film in comparison with the coherence length. Overall orientation of dyes in the film could be estimated from the experiments.