PhD Thesis Defense - High Resolution Spectroscopy of Environmentally Hazardous Gases at

April 3, 2008
9:00 am
Halligan 111-A
Speaker: Nawaf Almoayed, Tufts University, PhD student
Host: Prof Afsar

Abstract

Abstract:

The broadband dielectric properties of gases can be an extremely useful tool in identifying, characterizing, and detecting common pollutant gases. In particular, the absorption coefficient and refractive index spectra play an important role in this process due to the unique spectral signature of each gas. This study presents the unique absorption and refractive index spectra of pollutant gases at millimeter, submillimeter, and THz frequencies at varying pressures with unrivalled accuracy using high resolution dispersive Fourier transform spectroscopy. A one of a kind broadband polarizing interferometer was designed to test common pollutant gases in the millimeter, ubmillimeter, and THz wavelengths for this study. This setup has the capability to measure the dielectric properties of a sample gas from 60 GHz 1.2 THz. In order to fully understand and assess the rotational transition lines of pollutant gases, each gas was measured at differing pressures to get more insight into the behavior of the spectral lines with varying parameters. Absorption and Refractive index data for atmospheric pressure, Carbon Monoxide (CO), Carbon Dioxide (CO2), Sulfur Dioxide (SO2), and Nitrous Oxide (N2O) gas are presented and examined in this research. The aforementioned gases were specifically chosen due to the fact that they are common pollutant gases present in our atmosphere at any given time. The use of dispersive Fourier transform techniques in interferometry allows the measurement of absorption coefficient and refractive index spectra with great precision. Our measurements demonstrate that varying the pressure of the gas affects only the amplitude of the absorption lines and not their exact position. This is critical in air pollution studies when trying to single out a specific gas from a field sample with unknown constituents. These measurements and interpretations will be of great technical use in many areas, mainly environment monitoring and control, where submillimeter wave technology is making a significant impact.

Dissertaion Committee Members: Mohammed Afsar, Jeff Hopwood, Doug Preis, Jonathan Kenny, Chemistry Dept, and Dr. Igor Tkachov, Aware Inc