Structure-Property Relations for Nonlinear Optical Materials

An aggressive investigation is planned on the structure/nonlinear optical property relations of materials with special emphasis on several classes of organic compounds. An excellent collaborative team of experts has been assembled in this area along with the best experimental facilities for nonlinear optical (NLO) materials characterization. Along with the PI's at CREOL including a chemist, collaborators include Seth Marder, Joseph Perry and Jean-Luc Bredas with Chemistry at the University of Arizona, Francois Diederich in Chemistry at ETH, Zurich, Olga Przhonska, Alex Kachkovski and co-workers at the Institute of Physics, National Academy of Sciences, Kiev, Ukraine, and Anthony Brennan at the University of Florida. State-of-the-art laboratory facilities have been specifically designed and developed for the program outlined in this proposal. Five laboratories are devoted to this investigation. The latest addition is a femtosecond pump/continuum probe, nonlinear 'spectrophotometer'. This mimics the operation of a standard linear spectrophotometer and is the closest one can come to a facility that could be made into a commercial instrument for spectral analysis of NLO material properties. Data are consistent with the two-photon fluorescence (2PF) spectroscopy method, which takes considerably longer and requires fluorescent samples. Thus, a broader range of materials can be studied. These techniques, combined with the PIs' previously-developed experimental Z-scan technique, along with complementary methods of single frequency pump-probe methods with femtosecond, picosecond, and nanosecond tunable optical parametric sources, provide a unique facility to carry out the goals of this proposed effort. The ultimate goal of this study is to develop a predictive capability for the NLO properties in terms of the linear optical properties and/or molecular structure similar to what the PIs have accomplished for semiconductors. The femtosecond continuum can range in wavelength from 300 nm to >1.7 mm and can thus probe the NLA over this broad spectral range. Thus, in a single experiment the changes in absorption at all frequencies from the IR to the UV are measured. By temporally delaying the probe, the dynamics of this nondegenerate NLA are also obtained. This allows easy separation of the ultrafast NLA process of two-photon absorption from cumulative nonlinearities such as excited state absorption. With this instrument one can determine where are the strong two-photon absorption bands, and what is the excited-state absorption spectrum. The answers to these and similar questions will give theoreticians the information necessary to test theories and practitioners to find and exploit new NLO materials.