Sum Frequency Generation (SFG) is a powerful, nonlinear optical process, for probing interfaces-either buried or the more common air (or vacuum) interfaces. SFG produces complex spectra, where information about interfacial interactions and dynamics in the separate real and imaginary components are lost when the intensity-the absolute square of the surface response- is detected. An interference technique is required to probe the separate components; the most accurate instrument for interference measurements is an interferometer. However, due to the multiple inputs in nonlinear processes, both optical and conceptual issues require resolution to create a nonlinear interferometer. A designed and implemented nonlinear interferometer, dubbed a Shultz-Bisson-Wang (SBW) interferometer, has been applied to SFG. The instrument is highly stable due to active stabilization in the embedded linear Mach-Zehnder interferometer. The SBW interferometer has been applied to the SFG test surface octadecyltrichlorosilane (OTS), which does not have consistent spectra in the literature. The SBW interferometer enabled resolving C-H resonances due to the terminal methyl group, gauche defects, and the α-methylene group. The α-methylene resonances are weak, previously requiring deuterium substitution for the non-α-methylene hydrogen atoms to be identified. The α-methylene resonances are resolvable using the SBW interferometer on a standard silanized surface of OTS. Previously reported spectra differ due to varying balances among resonances of the three moieties indicating differing conformations. The role of water in this silanized surface has been studied using the SBW interferometer, as well as its application to liquid air interfaces.

Shultz-Bisson-Wang (SBW) nonlinear interferometer: Measuring complex sum frequency generation (SFG) spectra

256th National Meeting (2018)

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