Detection of Threat Materials Using Terahertz Waveguides and Long Pathlength Terahertz Spectroscopy.

摘要

This goals of this project are 1) to advance THz waveguide-based methods to measure and fundamentally understand THz vibrational spectra of threat materials, and 2) to create methods to propagate ultrashort THz pulses in the ambient atmosphere of long paths (> 100 meters) for detection of target vapors. Towards the first goal, significant progress was made generalizing the ability of THz waveguide spectroscopy to resolve previously undetected vibrational fingerprint resonances, in understanding the origin of the line narrowing effect at cryogenic temperatures, and in beginning to understand the effect of impurities on THz spectra. Towards the second goal, experimental work successfully demonstrated the propagation of ultrashort THz pulses over a record-long 170 meter path in ambient atmosphere with signal to noise detection as high as 200:1. The transmitted THz pulses were found to undergo reshaping from due to the strong interaction with atmospheric water vapor. The program demonstrated the feasibility of using THz pulses to detect small molecule threat vapors contained in the 170 meter path, through measurement of rotational signatures within the atmospheric transmission windows.