Electro-optic phase-modulated polarimetry: Instrumentation and signal analysis techniques for the characterization of material properties.

摘要

Novel compact and robust phase-modulated electro-optic birefringence and material stress measurement instrumentation is needed for the study of anisotropic materials such as non-Newtonian polymers, crystalline structures, biological fluids and many other optically active materials. This instrumentation developed by the research presented in this dissertation utilizes many different modulation approaches in order to incorporate heterodyning signal recovery techniques that improve measurement sensitivity by several orders of magnitude over simple crossed-polarizer methods. Modulation methods include photoelastic techniques, liquid-crystal variable retarder methods, dual-crystal transverse electro-optic modulation and dual lasers sinusoidally intensity-modulated with a π-phase lag between them.; The theoretical framework governing the development of this instrumentation using the Mueller-Stokes polarization matrices and heterodyning signal recovery methods is discussed in detail. Many experiments are performed to compare the measurements obtained by the instrumentation with the results derived theoretically. Results from the experimental material characterization instrumentation agree well with the predicted signal theory. Signal analysis was further refined through the use of wavelet-based denoising techniques. These denoising techniques resulted in improved measurement accuracy and sensitivity.; The measurement theory is also adapted to solve several other applications including electro-optic force, pressure and acceleration measurements which use a polymer linkage to infer stresses from the physical system to data that can be analyzed by the material characterization instrumentation. The best commercially available force transducers capable of measuring transient responses have a lower resolution of approximately 10−5 N. Research with the rheology of fluids, transient flows of pharmaceuticals in combinatorial research, biological tissue response, and biomimetic adhesive research often requires force measurements well below this range.; Full-field imaging applications that resolve material stresses over a specific area of the material under analysis have also been developed. The imaging techniques work by comparing polarization-modulated images at specified temporal frequencies synchronized to the modulation frequency. This technique provides a matrix of full-field gray level values corresponding to optical phase retardance and molecular orientation angle. The instrumentation can generate a matrix of these values at every resolvable point in a complex fluid or solid material being studied, whether the material is in transition or in a steady state.