This project studies the spectra of nonlinear optical (NLO) absorption and the dispersion of NLO refraction in a variety of materials types including classes of organic materials, nanocrystalline semiconductors and nanoparticles coupled to organic materials. The ultimate goals are to build a database of NLO properties of materials provided by researchers from around the world which, through collaboration with theorists, will lead to a predictive capability for these nonlinear processes that will also allow the determination of structure/NLO property relations. The PI has developed the experimental facilities for NLO materials characterization spanning a very large spectral (from the UV to 18mm) and temporal range (from femtosecond to nanoseconds). One of the workhorse tools that he has developed is a femtosecond pump/continuum probe, nonlinear "spectrophotometer" which measures the frequency nondegenerate NLO absorption spectrum along with its temporal response (critical for applying causality to determine Kramers-Kronig relations for the NLO refraction). The temporal response is useful for determining the source of the NLO response. In addition, he has very recently developed a "White-Light-Continuum Z-scan" (WLC Z-Scan). This method utilizes the broad spectrum of a femtosecond continuum pulse to directly measure the degenerate nonlinear absorption and separately measure the dispersion of the nonlinear refraction over a broad spectral range in a single experiment. The degenerate nonlinearities are often the ones of interest for applications, and this will allow for checks on the predictions of Kramers-Kronig relations. Intellectual merit: The experimental methodologies will provide a very large jump in the information database available for developing and understanding the fundamental bases for NLO interactions in multiple materials and material types. With this expanded database, observed trends will lead to scaling relations which lead to validation and/or modification of theory. At the same time this information provides feedback to materials researchers as to methods to enhance (or diminish) nonlinear responses. Broader impacts: This project will partially fund the training of three Ph.D. students (2 on NLO and one in organic synthetic chemistry) as well as several undergraduate students through the NSF Research Experiences for Undergraduates program. An additional graduate student, funded through Co-PI Hagan's NSF GK-12 program, will work with teachers in local schools on the development of Optics content in the 9th grade science curriculum. The curricula of two graduate optics courses (Fundamentals of Optical Science and Nonlinear Optics) have been enriched by incorporation of information from this work.
