Spatial Pattern Separation of Chemicals and Frequency-Independent Components by Terahertz Spectroscopic Imaging

We separated the component spatial patterns of frequency-dependent absorption in chemicals and frequencyindependent components such as plastic, paper, and measurement noise in terahertz (THz) spectroscopic images, using known spectral curves. Our measurement system, which uses a widely tunable coherent THzwave parametric oscillator source, can image at a specific frequency in the range 1 -2 THz. The component patterns of chemicals can easily be extracted by use of the frequency-independent components. This method could be successfully used for nondestructive inspection for the detection of illegal drugs and devices of bioterrorism concealed, e.g., inside mail and packages.