Nonlinear Optical Properties of Azo Dye Monolayers:The Effect of Tilt Angle on the Local Field

We report on the second-order nonlinear optical susceptibility chi(2)(2omega,omega,omega) of dye-doped Langmuir-Blodgett monolayers. Chi(2) is found to exhibit a nonlinear dependence on surface density, which is attributed to microscopic local-fields. In order to calculate the microscopic local-field for the disordered systems, a novel Monte-Carlo type of calculation is described, in which the tilt angle of the dye unit is a sensitive parameter. It is shown also that the tilt angle of rod-shaped chromophores in Langmuir-Blodgett films can be measured by angular-dependent absorption measurements.