Engineering metal parallel plate waveguides as a 2-D plane for high resolution THz time domain spectroscopy
Abstract
Scope and Method of Study: The research summarized in this dissertation is on the investigation of the application of metal parallel plate waveguides (PPWG) for performing high resolution spectroscopic measurements of molecular solids at THz frequencies. The dissertation also presents results on the incorporation of high Q periodic structures within a metal PPWG and their application in sensitive detection of materials by monitoring change in refractive index. The experimental results were obtained by measuring the transmission of metal PPWG with samples in a standard THz time domain spectroscopy system based on photoconductive switches in 4f geometry. Findings and Conclusions: The main finding of this endeavor is that waveguide THz time domain spectroscopy using metal PPWGs can be efficiently applied to extract high resolution vibrational resonances associated with molecular solids. This technique discovered as a part of this research is a new and novel method which for the first time facilitates high resolution spectroscopic measurements of solid microcrystalline films which are easy to make in comparison to single crystal samples, but allows us to extract high resolution vibrational modes of the molecules. This technique can be complimentarily applied with the standard THz-TDS and Fourier transform infra-red spectroscopy to resolve the complete vibrational response of any molecular solid. We have also shown that metal PPWG also allows the incorporation of periodic structures like a weak Bragg stack and be applied as a very high - Q frequency filter having application in chemical sensing. The Q factors obtained by us are among the highest obtained for resonant and periodic structures within waveguide structures. We can conclude that the PPWG acts as an efficient 2-D plane which allows for performing high resolution spectroscopy and for incorporating frequency filtering devices with in the sub wavelength gap.
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- OSU Dissertations [11222]