Nonlinear optical spectroscopy and microscopy

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This research program will focus on applications of several new nonlinear optical techniques to study surface chemistry and to develop microscopy for high-resolution three-dimensional imaging and chemical composition analysis. (1) Study of Surface Chemistry Using IR-visible Sum Frequency Generation (SFG) Many important chemical processes occur at a gas/solid or liquid/solid interface. The study of these interfaces requires a tool that has enough sensitivity to probe a sub-monolayer of molecules on the interfaces without the interference from the gas or liquid. SFG has several advantages over traditional spectroscopic techniques, such as IR and Raman spectroscopy, because SFG is intrinsically surface-specific when the media have inversion symmetry, such as gas or liquid. It is a fast-evolving technique well positioned to have significant contributions to surface chemistry research. New developments in polarization modulation SFG and two-dimensional SFG will be introduced to study surface chemistry, including surface phase transitions of polymers and electrochemical catalytic reactions. (2) Nonlinear Optical Microscopy and Its Applications in Chemistry and Biology      Since their invention in the 16th century, microscopes have allowed scientists to see tiny structures that are not visible to the naked eye and have allowed countless discoveries to be made that have provided underpinnings to broad areas of science. Nonlinear optical imaging has several advantages over linear optical imaging including better spatial resolution and better contrast. We will develop microscopy based on nonlinear optical processes, such as coherent anti-Stokes Raman scattering (CARS), second harmonic generation (SHG), and third harmonic generation (THG), for high-resolution imaging and chemical composition analysis.