Nonlinear Optical Stokes Ellipsometry. 2. Experimental Demonstration

Abstract

Second harmonic generation (SHG) has developed into a powerful tool for characterizing oriented thin films, surfaces, and interfaces. Furthermore, the nonlinear optical nature of wave-mixing processes typically results in the generation of a coherent signal beam with a well-defined polarization state. This coherence offers unique opportunities for the extraction of detailed molecular and surface properties from polarization analysis. In previous studies, nonlinear optical ellipsometry (NOE) has been developed as a means to retain sign and phase information between the different nonzero χ (2) tensor elements present in a given sample. However, those previous methods and related approaches for polarization analysis have all relied on the physical movement of optical elements to perform the analysis. The time required to physically move the appropriate optical elements ultimately dictates the fastest analysis time possible in a given technique. Such long acquisition times have limited NOE analyses to systems exhibiting excellent photostability and have precluded the feasibility of NOE imaging. Development of nonlinear optical Stokes ellipsometry (NOSE) was shown to address many of these problems. By increasing the repetition rate of the laser system and replacing previously slow rotating polarization optics with a rapid photoelastic modulator, the acquisition time with full polarization analysis was reduced from several hours to less than a second. This technique was validated against established NOE techniques using z-cut quartz as a reference sample and then demonstrated on a dye thin film. Additionally, an orientation analysis of the thin film was performed. These studies resulted in an order of magnitude improvement in precision relative to previous NOE techniques, while simultaneously accompanied by a reduction in acquisition time of more than four orders of magnitude.

Modeling multilayer thin film interference effects in interface-specific coherent nonlinear optical spectroscopies

“…We envision that this model will have implications in a wide range of problems as straightforward as rational experimental design to some of the more vexing challenges in surface specific spectroscopy, such as quantification of bulk contributions or microscopic local field corrections (i.e., local dipole effects) [30][31][32]. Further, we see this as a step forward for such techniques as nonlinear ellipsometry [33,34] on thin film systems. We have presented equations that allow for a multitude of experimental geometries.…”

Second-Order Nonlinear Optical Imaging of Chiral Crystals

“…However, this sensitivity is also a largely unexploited tool for characterizing crystal polymorphism and orientation. The recent development of high-precision polarization-dependent measurement approaches that are compatible with SHG microscopy techniques (65–67), in combination with theoretical and computational tools to aid in polarization analysis (14), has the potential to bridge macroscopic observables with microscopic structure and orientation. These capabilities may aid the identification of domain boundaries within crystals, including those from twinning.…”

Polarization-resolved second-harmonic generation microscopy as a method to visualize protein-crystal domains

“…PR-SHG measurements of monolayers at interfaces have previously been shown to enable discrimination between samples with similar nonlinear optical properties (Begue, Everly et al, 2009;Begue & Simpson, 2010;Begue, Moad et al, 2009). Further, polarization-dependent SHG microscopy has a rich history of enabling structural and orientational studies Amat-Roldan et al, 2010;Chang et al, 2011;Latour et al, 2012;Duboisset et al, 2012;Stoller et al, 2002;Mansfield et al, 2007;Nucciotti et al, 2009;Filippidis et al, 2009;Madden et al, 2011;Tuer et al, 2011;Brideau & Stys, 2012).…”