Analysis of linear and quadratic optical response of mixed Langmuir-Blodgett films of stearic acid and 5-CT

Published experimental optical second-harmonic generation (SHG) results for mixed films formed between stearic acid and the mesogen 5-CT (4"-n-pentyl-4-cyano-p-terphenyl) are reanalyzed. Experimental refractive index results for the pure films are used to deduce molecular polarizabilities in order to calculate local fields. At low and high fractions of 5-CT, a consistent interpretation of the SHG is obtained using a mean molecular response based on a fixed axial hyperpolarizability beta (LLL) for the mesogen, but at high mesogen fractions molecular tilt makes small off-diagonal components beta (LLM)approximate to-beta (LLL)/40 essential. At intermediate fractions the treatment can interpret the SHG only by requiring molecular tilt not found in the experiments, implying that a more detailed structural model is required. (C) 2000 American Institute of Physics. [S0021- 9606(00)70247-9].