Ionically self-assembled second order nonlinear optical thin-film materials and devices

We report that a new ionically self-assembled monolayer (ISAM) method for thin-film deposition can be employed to fabricate materials possessing the noncentrosymmetry that is required for a second order, chi((2)), nonlinear optical response. Using several different commercially-available polyelectrolytes and additional precursors designed and fabricated in our laboratories, we have produced ISAM nonlinear optical thin films with chi((2)) values greater than that of quartz. As a result of the ionic attraction between successive layers, the ISAM chi((2)) films self-assemble into a noncentrosymmetric structure that has exhibited no measureable decay of chi((2)) at room temperature over a period of more than four months. The chi((2)) of ISAM thin-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 of fundamental intensity and film thickness while the polarization dependence is consistent with orientation of the chromophore dipole moment perpendicular to the substrate. We describe the potential application of such NLO thin-film materials in field sensing elements and support instrumentation systems.