Absorption of THz Radiation by Atmospheric Water Vapor

Abstract

<p>THz radiation is electromagnetic radiation that exists between the microwave and the infrared regions of the electromagnetic spectrum. It is non-ionizing radiation and can penetrate through materials that are opaque to visible light so therefore has many new and exciting applications. Systems employing THz radiation are becoming more common. Due to water vapor, Earth's atmosphere heavily attenuates THz radiation in certain regions and therefore represents a challenge to communications and sensing applications at these frequencies. The theory of how the atmosphere attenuates propagating THz radiation by absorption and scattering will be discussed. The absorption of THz radiation by water vapor was measured at 325 and 620 GHz using frequency domain absorption spectroscopy. Spectral line shapes were recorded across a range of pressures and fitted to Voigt profiles. The resulting relationship between the line width and pressure was shown to be linear and in agreement with published values. The transient signals associated with population and polarization relaxation times were also measured at 325 GHz using time domain spectroscopy techniques. Experimental results associated with the frequency and time domain measurements will be discussed.</p><p>This presentation occurred at the Wright State University Campus-Wide Celebration of Research, Scholarship and Creative Activities on April 16, 2010</p>