Polarization analysis in nonlinear optics and multiphoton microscopy
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 the 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 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 the relative sign and phase information between the different nonzero χ(2) tensor elements present in a given sample. However, those methods and related approaches for polarization analysis have all relied on the mechanical movement of optical elements in order 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 (generally several hours for full ellipsometric detection). Such long acquisition times have limited NOE analysis to systems exhibiting excellent photostability and frustrated attempts at kinetics and microscopy applications. Development of nonlinear optical Stokes ellipsometry (NOSE) is described and developed in this thesis to alleviated 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 has been reduced from several hours to a fraction of a second. This more than four order of magnitude reduction in acquisition time is accompanied by an order of magnitude increase in precision in the χ(2) tensors than previously achieved. These improvements have enabled imaging with full ellipsometric analysis at each pixel, allowing a unique contrast mechanism based on principle component analysis of the polarization dependent signal. Additionally insight into crystal quality for x-ray diffraction studies and orientation of chiral crystals is accessible.
Degree
Ph.D.
Advisors
Simpson, Purdue University.
Subject Area
Analytical chemistry
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