Terahertz wave reference-free phase imaging for identification of explosives

We present terahertz reference-free phase imaging for identification of three explosive materials (HMX, RDX, and DNT. We propose a feature extraction technique to locate the spectral position of an unknown material's absorption lines without using the reference signal. The samples are identified by their absorption peaks extracted from the negative first-order derivative of the sample signal phase divided by the frequency at each pixel. This technique will greatly benefit the future development of standoff distance, large size focal-plane terahertz imaging system. (C) 2008 American Institute of Physics.