In gas spectroscopy, chemicals can be identified by the set of frequencies at which their absorption lines occur. The concentration can be quantitatively estimated from the intensity of any of the absorption lines. The sensitivity of the spectrometer, i.e., the minimum detectable concentration, is ideally limited by the ratio of the source power to detector noise-equivalent power. In practice, the sensitivity is usually orders of magnitude worse due to systematic effects. In this work we built a simple gas terahertz transmission spectrometer to analyze how the source output power stability, the detector sensitivity, and atmospheric pressure affect its sensitivity. As a test gas we used methyl chloride in a mixture with air and modifid the widths of the absorption lines by changing partial pressure of air. This demonstration of a simple absorption spectrometer gives us insight into the approach to making a highly sensitive terahertz spectrometer.
Proceedings Title: Proc. of SPIE
Volume: Vol. 6949
Conference Dates: March 18-21, 2008
Conference Location: Orlando, FL
Conference Title: SPIE - The International Society for Optical Engineering, Defense & Security Symposium
Pub Type: Conferences
Spectroscopy, methyl chlorde, linewidth, pressure broadening.