Ryan M. Plocinik

Polarization characterization in surface second harmonic generation by nonlinear optical null ellipsometry

Abstract Nonlinear optical null ellipsometry (NONE) is developed as a novel approach to evaluate second-order nonlinearities on and off resonance in transparent and absorbing thin surface films. Despite the growing use of second harmonic and sum frequency spectroscopy in characterizing interfaces, common approaches designed to extract the χ(2) nonlinear susceptibility tensor elements from relative intensity measurements are generally only reliable for ultra-thin transparent films at the interface between transparent media. The simple expressions routinely used to treat intensity-based polarization measurements far from resonance become significantly more complicated on or near resonance, for which the χ(2) tensor elements and the thin film refractive indices are complex-valued parameters. In contrast, the mathematical formalism developed for NONE measurements is well suited for spectroscopic studies. The combined results of NONE and polarization-dependent intensity (PDI) measurements at fused silica/dye solution interfaces demonstrate that NONE retains complex phase information between the χ(2) nonlinear susceptibility tensor elements that is lost using comparable intensity-based approaches.

Discrete retardance second harmonic generation ellipsometry

A new instrument was constructed to perform discrete retardance nonlinear optical ellipsometry (DR-NOE). The focus of the design was to perform second harmonic generation NOE while maximizing sample and application flexibility and minimizing data acquisition time. The discrete retardance configuration results in relatively simple computational algorithms for performing nonlinear optical ellipsometric analysis. NOE analysis of a disperse red 19 monolayer yielded results that were consistent with previously reported values for the same surface system, but with significantly reduced acquisition times.

Exploiting polarization in nonlinear optical surface spectroscopy

Combining nonlinear optics with ellipsometry improves the information content available in studies of nonlinear optical surfaces and materials and provides a novel and general route for background suppression. As one example, this novel nonlinear optical null ellipsometry (NONE) approach allowed for the selective detection of bovine serum albumin adsorption on glass from the changes induced in the hyperpolarizability of coadsorbed rhodamine 6G, providing a general route for label-free real-time biosensing. In combination with new theoretical developments, polarization analysis in surface second harmonic generation is shown to yield rich information on molecular orientation and the optical constants of the thin surface layer. This ellipsometric technique is particularly useful in studies of chiral media, in which second-order nonlinear optical measurements have been shown to be remarkably sensitive to chirality at the interface.

Nonlinear Optical Ellipsometric Studies of Chiral Systems

Nonlinear optical ellipsometry (NOE) was developed to interpret polarization information of the second harmonic generated (SHG) light at thin surface films. The experimentally simple instrument design allows for a mathematically straightforward evaluation of the data and yields greater information content than comparable intensity based techniques. The polarization- dependence of the SHG light yields the fully complex valued set of χ(2) nonlinear susceptibility tensor elements. The χ(2) tensor elements can then be related back to the structure of molecules at the silica/aqueous solution interface.