Abstract

The reflection spectrum of the explosive RDX was acquired from a diffuse reflection measurement using a THz time-domain spectroscopy system in combination with a diffuse reflectance accessory. By applying the Kramers-Kronig transform to the reflection spectrum, the absorption spectrum (0.2–1.8 THz) was obtained. It agrees with the result from a transmission measurement and distinguishes RDX from other materials. The effect of the reference spectrum was examined by using both a Teflon pellet and a copper plate as references. The strong absorption of RDX at 0.82 THz allowed it to be identified by the diffuse reflection measurement even when the RDX sample was covered with certain optically opaque materials. Our investigation demonstrates that THz technique is capable of detecting and identifying hidden RDX-related explosives in a diffuse reflection mode, which is crucial for the standoff detection in the real world applications.

© 2006 Optical Society of America

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References

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Appl. Phys. Lett. (5)

F. Huang, B. Schulkin, H. Altan; J. F. Federici, D. Gary, R. Barat, D. Zimdars, M. Chen and D. B. Tanner, "Terahertz study of 1,3,5-trinitro-s-triazine by time-domain and Fourier transform infrared spectroscopy," Appl. Phys. Lett. 85, 5535-5537 (2004).
[CrossRef]

Y. C. Shen, T. Lo, P. F. Taday, B. E. Cole, W. R. Tribe and M. C. Kemp, "Detection and identification of explosives using terahertz pulsed spectroscopic imaging," Appl. Phys. Lett. 86, 241116 (2005)
[CrossRef]

Q. Wu, M. Litz, and X.-C. Zhang, "Broadband detection capability of ZnTe electro-optic field detectors," Appl. Phys. Lett. 68, 2924-2926 (1996).
[CrossRef]

Y. C. Shen, P. C. Upadhya, H. E. Beere, E. H. Linfield, A. G. Davies, I. S. Gregory, C. Baker, W. R. Tribe and M. J. Evans, "Generation and detection of ultrabroadband terahertz radiation using photoconductive emitters and receivers," Appl. Phys. Lett. 85, 164-166 (2004)
[CrossRef]

S. Nashima, O. Morikawa, K. Takata and M. Hangyo, "Measurement of optical properties of highly doped silicon by terahertz time domain reflection spectroscopy," Appl. Phys. Lett. 79, 3923-3925 (2001).
[CrossRef]

Chem. Phys. Lett. (1)

Y. Chen, H. Liu, Y. Deng, D. Schauki, M. J. Fitch, R. Osiander, C. Dodson, J. B. Spicer, M. Shur and X. C. Zhang, "THz spectroscopic investigation of 2,4-dinitrotoluene," Chem. Phys. Lett. 400, 357-361 (2004).
[CrossRef]

J. Appl. Phys. (1)

E. M. Vartiainen, Y. Ino, R. Shimano, M. Kuwata-Gonokami, Y. P. Svirko and K.-E. Peiponen, "Numerical phase correction method for terahertz time-domain reflection spectroscopy," J. Appl. Phys. 96 (8), 4171-4175 (2004).
[CrossRef]

J. Biol. Phys. (2)

M. R. Scarfi, M. Romanò, R. Di Pietro, O. Zeni, A. Doria, G. P. Gallerano, E. Giovenale, G. Messina, A. Lai, G. Campurra, D. Coniglio and M. D' Arienzo, "THz exposure of whole blood for the study of biological effects on human lymphocytes," J. Biol. Phys. 29, 171-177 (2003).
[CrossRef]

R. H. Clothier and N. Bourne, "Effects of THz exposure on human primary keratinocyte differentiation and viability," J. Biol. Phys. 29, 179-185 (2003).
[CrossRef]

Jpn. J. Appl. Phys. (1)

K. Yamamoto, M. Yamaguchi, F. Miyamaru, M. Tani, M. Hangyo, T. Ikeda, A. Matsushita, K. Koide, M. Tatsuno and Y. Minami, "Noninvasive inspection of C-4 explosive in mails by terahertz time-domain spectroscopy," Jpn. J. Appl. Phys. 43, 414-417 (2004).
[CrossRef]

Opt. Lett. (1)

Proc. SPIE (3)

T. Yuan, H. Liu, J. Xu, F. Al-Douseri, Y. Hu and X.-C. Zhang, "Terahertz time-domain spectroscopy of atmosphere with different humidity," in Terahertz for Military and Security Applications, R. J. Hwu and D. L. Woolard, eds, Proc. SPIE 5070, 28-37 (2003).

M. C. Kemp, P. F. Taday, B. E. Cole, J. A. Cluff, A. J. Fitzgerald and W. R. Tribe, "Security applications of terahertz technology," in Terahertz for Military and Security Applications, R. J. Hwu and D. L. Woolard, eds, Proc. SPIE 5070, 44-52 (2003).
[CrossRef]

Y. Chen, H. Liu, Y. Deng, D. Veksler, M. Shur, X. -C. Zhang, D. Schauki, M. J. Fitch and R. Osiander, "Spectroscopic characterization of explosives in the far infrared region," in Terahertz for Military and Security Applications II, R. J. Hwu and D. L. Woolard, eds, Proc. SPIE 5411, 1-8 (2004).
[CrossRef]

Rev. Sci. Instrum. (2)

M. Khazan, R. Meissner and I. Wilke, "Convertible transmission-reflection time-domain terahertz spectrometer, " Rev. Sci. Instrum. 72, 3427-3430 (2001).
[CrossRef]

A. Pashkin, M. Kempa, H. Nemec, F. Kadlec and P. Kuzel, "Phase-sensitive time-domain terahertz reflection spectroscopy, " Rev. Sci. Instrum. 74, 4711-4717 (2003).
[CrossRef]

Other (3)

F. Stern, Solid Sate Physics, edited by F. Seitz and D. Turnbull (Academic Press, Inc., New York, 1963) 15, 299.
[CrossRef]

F. M. Mirabella, Modern Techniques in Applied Molecular Spectroscopy, (John Wiley & Sons, 1998), Chap. 3.

F. M. Mirabella, Modern Techniques in Applied Molecular Spectroscopy, (John Wiley & Sons, 1998), Chap. 5.

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Figures (5)

Fig. 1.
Fig. 1.

Rough sample surface results in diffuse reflection. Specular reflection, indicated by the solid lines, has a reflection angle equal to the incident angle. Diffuse reflections, denoted by the dashed lines, have reflection angles that are independent of the incident angle.

Fig. 2.
Fig. 2.

A planform of THz-TDS with a diffuse reflectance accessory.

Fig. 3.
Fig. 3.

(a) Relative power reflection spectra of RDX, polyethylene and flour, the diffuse spectrum of Teflon was used as reference; (b) Absorption spectra of RDX, polyethylene and flour from the K-K transform of the reflection spectra; (c) The comparison between the absorption spectra from the transmission measurement (upper curve) and diffuse reflection measurement (bottom curve); (d) Absorption spectra of 3 different RDX samples. All the measurements were conducted in nitrogen atmosphere to avoid the effect of water vapor absorption in ambient air. The dashed lines indicate the absorption peak positions.

Fig. 4.
Fig. 4.

Absorption spectra of RDX from the K-K transform of the reflection spectra using Teflon as reference and copper as reference respectively. The dashed lines indicate the absorption peak positions.

Fig. 5.
Fig. 5.

(a) A comparison between the absorption spectra of RDX obtained from the diffuse reflection measurements when RDX was bare and was covered with paper; (b) Absorption spectra of RDX obtained from the diffuse reflection measurements under different covers. Upper curve: polyethylene sheet cover; middle curve: leather cover; bottom curve, polyester cloth cover. The dashed lines indicate the absorption peak positions.

Equations (5)

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r = Re
θ ( v 0 ) = 2 v 0 π P 0 ln R ( v ) v 2 v 0 2 dv
n = 1 R 1 + R 2 R cos θ
k = 2 R sin θ 1 + R 2 R cos θ
α = 4 πvk c

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