Polarization effects in nonlinear optics
Abstract
Second-order nonlinear optical techniques have been used to study the structure, orientation and kinetics of molecules at surfaces. Research has been focused on the development of new tools for simplifying the determination of this information from experiments, predicting it from theory, and investigating the origin of the phenomena. Experiments have been made to support the hypothesis that molecular orientation drives the large chiral response measured in second harmonic generation (SHG). Theoretical predictions have been made to show that magnetic dipole contributions are small. Software has been developed to extract surface tensor and orientation information from SHG experiments. An intuitive way of interpreting nonlinear optical and multiphoton processes in terms of products of lower order effects has been implemented. Symmetry analysis has been employed to create nonlinear character tables for SHG, sum frequency generation (SFG) and progress is being made for coherent anti-Stokes Raman spectroscopy. A software program named NLOPredict has been developed that can open molecular coordinate files in the protein database (.pdb) format and take input nonlinear optical tensor data. The transition dipole moment and transition polarizability tensor are then displayed on top of the molecule as a line vector and tensor glyph, respectively. Since the nonlinear optical response is sensitive to the orientation of the molecule the user can rotate it around and see the predicted surface response change. Default values can also be used to predict the nonlinear optical properties for entire proteins. The time required to make a SHG measurement with full polarization analysis can be many hours. This limits the types of samples that can be analyzed. A new fast-SHG instrument has been constructed to speed up this time to 100 μs for materials and 1 s for a single monolayer.
Degree
Ph.D.
Advisors
Simpson, Purdue University.
Subject Area
Analytical chemistry
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