Microscopic calculations of linear and quadratic optical response in modelLangmuir-Blodgett multilayers

Microscopic calculations are reported of linear and quadratic nonlinear opt ical response in Langmuir-Blodgett films. The films are modeled as ordered layers of molecules that can tilt from the vertical and have a higher polar izability and first hyperpolarizability in the head than in the tail. The l ocal electric field varies little after the first layer and negligibly afte r the second, which simplifies the analysis. Tilted two-layer Y-type films can have quadratic susceptibility components as large as X- or Z-type ones. Overall the results provide a systematic account of the linear and nonline ar optical properties as a function of molecular and film structure that sh ould assist interpretation of experimental results. (C) 2000 American Insti tute of Physics. [S0021- 9606(00)70115-2].