Werner Hickel

Langmuir-Blodgett films for optical applications

Abstract Langmuir-Blodgett films exhibit interesting properties which make them promising materials for application in second order-nonlinear optics. However, there are still some problems to solve. One of these is to maintain the good orientation of chromophores found in monolayers also in noncentrosymmetric multilayer films. Another issue is to prepare Langmuir-Blodgett films that form low optical loss waveguides. In this paper we show that these problems can be overcome by using specifically designed compounds. So for multilayer films with alternating monolayers from a nitrophenylhydrazone dye and a polymerizable amphiphile a quadratic increase of second harmonic intensity with increasing film thickness was found. This proves that the orientation of the dyes remains unchanged in the noncentrosymmetric multilayer. Langmuir-Blodgett film waveguides with low optical losses were obtained from a prepolymerized amphiphile which has flexible side chains that cannot crystallize and thus prevent domain formation within the monolayer. Multilayer films consisting of 500 monolayers from that compound exhibit a light attenuation as low as 2 dB/cm for 633 nm light.