Date of Award

4-1-1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Abstract

The primary objective of this research is the design and application of a stationary mask Hadamard transform infrared (HT-IR) spectrometer. Previous research in the area of stationary Hadamard encoding focused on the use of switching materials for the masks. However, these masks could not pass infrared radiation and, as a result, the advantages of stationary Hadamard encoding could not be applied to infrared spectrometry. A nontraditional mask, called a thermo-optic array for the stationary encoding of radiation (TOASTER), was proposed and implemented to perform the stationary Hadamard encoding. The Hadamard encoding procedure was performed with an array of electrically controlled IR sources. Operated with a reversed Czerny-Turner system, the source array was switched on or off according to the Hadamard functions. In this manner, the wavelength limitation to stationary Hadamard encoding was totally lifted.The research presented in this dissertation addresses two other aspects of stationary mask HT-IR. First, since the optical encoding of the TOASTER was thermally operated, the thermo-optic behavior of the electrically controlled IR sources was studied based on the theory of heat conduction. Secondly, a LiTaO$\sb3$ pyroelectric detector was employed in our prototype HT-IR spectrometer and as a result, the feasibility of low cost pyroelectric IR detectors for spectrometric use was investigated and discussed.The results of this work showed that the thermo-optic array and the corresponding optical design of the HT-IR could allow the prototype instrument to work in the IR region with a transform multiplex advantage. The thermo-optic stationary encoding method also provided frequency precision with experimental results of spectral subtraction. With regards to the thermo-optic behavior of the electrically controlled IR sources, the experimental data verified the physical and mathematical analysis proposed. In addition, the low cost pyroelectric IR detector, with proper signal processing, was found to be useful for spectrometric use under certain application requirements.

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