| A new second harmonic generation (SHG) nonlinear optical ellipsometry (NOE) technique was developed based on discrete retardance (DR) measurements using fixed wave plates, as opposed to continuously rotating optical elements. The focus of the design was to perform NOE while maximizing sample and application flexibility, minimizing data acquisition time, and simplifying the data analysis process. NOE performed on a disperse red 19 monolayer yielded results that were consistent with previously reported values, and when scaled for the shorter acquisition times, the DRNOE measurements were comparable in precision to other NOE methods.;The DR-NOE technique was also used to study surface kinetics and characterize macroscopic materials. First, the kinetics of dithiocarbamate (DTC) monolayer formation on gold substrates was measured in situ in real-time by SHG. The assembly kinetics and saturation coverages were found to be similar to those of alkanethiols on gold. However, the rate of adsorption did not change with DTC concentration in a manner expected of Langmuir kinetics. Second, SHG polarization analysis was performed on electrochemically assembled collagen molecules and reference samples. The collagen fibrils within the macroscopic collagen fibers were determined to be largely aligned and oriented. Third, SHG was used to monitor the real-time enzymatic degradation of a corn stover fiber. SHG polarization analysis was also used to detect differences in the cellulose structure after the native corn stover fiber was pretreated and enzymatically degraded. Lastly, the DR-NOE technique was integrated into a scanning sum-frequency generation system. Preliminary spectra were obtained for crystalline lysine, ibuprofen, and sucrose samples. |
