Second-order nonlinear optical thin films fabricated from ionically self-assembled monolayers

Abstract

We demonstrate, for the first time, that a new ionically self-assembled monolayer (ISAM) technique for thin film deposition can be employed to fabricate materials possessing the noncentrosymmetry that is requisite for a second order, nonlinear optical response. Using two different commercially-available polyelectrolytes, we have produced ISAM nonlinear optical thin films with values comparable to that of quartz. As a result of the ionic attraction between successive layers, the ISAM films self-assemble into a noncentrosymmetric structure that has exhibited no measureable decay of at room temperature over a period of more than four months. The x2 of ISAM films has been examined by second harmonic generation using a fundamental wavelength of 1200 nm. The second harmonic intensity of the films exhibits the expected quadratic dependences on fundamental intensity and film thickness while the polarization dependence is consistent with orientation of the chromophore dipole moment perpendicular to the substrate.