Terahertz Reflection Spectroscopy And Imaging

Terahertz (THz) technology has been widely applied in far-infrared spectral measurement of chemical compounds. This method enables standoff-distance detection of explosive materials, bio-medical inspection and illicit drug examination. In traditional reflective absorption spectrum measurements, Fresnel equations are used to extract the absorption features of the samples. However, the height difference between the target and reference surfaces introduces significant phase shift errors in the final result. Methods that have been proposed to eliminate the phase error usually involves big amount of calculation or nitrogen purged environment. We present a novel feature extraction technique for identification of explosive and biological materials using terahertz reflection time domain spectroscopy (THz-RTDS). The absorption signatures of the materials are extracted directly from the derivative of the ratio of the reflection.In this thesis, a reflective THz spectroscopy system was built, data acquisition program was made using Labview Software and pattern recognition tasks were performed on the measured data using a Matlab code. Three explosive samples-HMX, 2, 4-DNT, RDX have been investigated by the THz reflection pulsed imaging system. The result indicates that by using this new method, one can get the specific absorption peaks of these three explosive samples in the THz range under a relatively higher humidity condition. Pattern recognition results further confirm that this method is valid to be used for spectroscopic imaging at a standoff distance, without considering the phase difference. This technique provides a straightforward and fast solution to solve the phase-retrieval problem in RTDS and will benefit the future development of standoff, large size focal-plane THz sensing and imaging system.