Compared to other parts of the spectrum, the application of terahertz waves is still in it's infancy. However, its ability to penetrate through many common non-metallic materials and provide material specific information has made terahertz waves a compelling option for non-destructive testing, and stand-off evaluation of materials (such as explosives detection).

Security and Defense Applications - Explosives Detection

Recently, THz spectroscopy and imaging of ERCs have been investigated intensively for possible defense and security applications. In 2003, Kemp et al.¹ reported measurements showing THz spectral features in a number of common energetic explosives, such as 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), pentaerythritol tetranitrate (PETN), and commercial explosives like PE-4 and Semtex. Subsequently, Chen et al.² reported a THz spectra of 14 ERCs obtained by both THz time-domain spectroscopy (THz-TDS) and Fourier-transform far-infrared spectroscopy. Yamamoto et al.³ and Huang et al.⁴ reported the THz absorption of RDX validating the results of Kemp et al. While these experiments were conducted using transmission mode THz-TDS, work on using real-work applicable reflection geometry measurements has also been investigated. Detection of RDX by THz specular reflection spectroscopy has been demonstrated recently by Shen et al.⁵ . Investigation the THz diffused reflection spectra of explosives using RDX as a model compound suggest that THz diffused reflection spectroscopy has a great potential for the detection and identification of explosives concealed in packages or under clothing⁶. In addition, the Center for Terahertz Research at Rensselaer Polytechnic Institute has successfully sensed RDX by THz specular reflection spectroscopy at a standoff distance of 30 m⁷.

Non-destructive testing (NDT)

Terahertz techniques are also useful for non-destructive testing applications, since both material and structural information can be obtained using CW and Time Domain systems. Terahertz imaging is one of two techniques that is being applied to look for defects and voids in the insulating foam on the Space Shuttle's external tank. It has also been proven useful in characterizing fire damage in carbon fiber composites in use on airplanes. From measuring coatings on medicines to identifying polymorphs and hydrates in drug compounds, there are numerous applications in the pharmaceutical industry as well. If you have a NDT problem, we can help you evaluate THz techniques as a potential solution.

1. Security applications of terahertz technology, M. C. Kemp, P. F. Taday, B. E. Cole, J. A. Cluff, A. J. Fitzgerald, and W. R. Tribe, Proc. SPIE, vol. 5070, pp. 44-52, 2003.
2. "Spectroscopic characterization of explosives in the far-infared region," Y. Chen, H. Liu, Y. Deng, D. Veksler, M. Shur, X.-C. Zhang, D. Schauki, M. J. Fitch, and R. Osiander. Proc SPIE, vol 5411, pp. 1-8, 2004
3. Noninvasive inspection of C-4 explosive in mails by terahertz time-domain spectroscopy, K. Yamamoto, M. Yamaguchi, F. Miyamaru, M. Tani, M. Hangyo, T. Ikeda, A. Matsushita, K. Koide, M. Tatsuno, and Y. Minami,Jpn. J. of Appl. Phys. vol. 43, pp. L414-417, 2004.
4. Terahertz study of 1,3,5-trinitro-s-triazine by time-domain and Fourier transform infrared spectroscopy, F. Huang, B. Schulkin, H. Altan; J. F. Federici, D. Gary, R. Barat, D. Zimdars, M. Chen, and D. B. Tanner, Appl. Phys. Lett., vol. 85, pp. 5535-5537, 2004.
5. Detection and identification of explosives using terahertz pulsed spectroscopic imaging, Y. C. Shen, T. Lo, P. F. Taday, B. E. Cole, W. R. Tribe, and M. C. Kemp, Appl. Phys. Lett., vol. 86, pp. 241116, 2005.
6. Detection and identification of explosive RDX by THz reflection spectroscopy, H. B. Liu, Y. Chen, G. J. Bastiaans, and X.-C. Zhang, Optics Express, 14, 415-423 (2006)
7. THz standoff detection of explosive RDX, H. Zhong, A. Redo, Y. Chen and X.-C. Zhang, THz/IRMMW 2005, Williamsburg, VA, 2005