Abstract

We demonstrate a tomographic imaging modality that uses pulsed terahertz (THz) radiation to probe the optical properties of three-dimensional (3D) structures in the far-infrared. This THz-wave computed tomography (T-ray CT) system provides sectional images of objects in a manner analogous to conventional CT techniques such as x-ray CT. The transmitted amplitude and phase of broadband pulses of THz radiation are measured at multiple projection angles. The filtered backprojection algorithm is then used to reconstruct the target object, including both its 3D structure and its frequency-dependent far-infrared optical properties.

© 2002 Optical Society of America

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References

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  1. B. B. Hu and M. C. Nuss, Opt. Lett. 20, 1716 (1995).
    [CrossRef]
  2. Q. Wu, T. D. Hewitt, and X.-C. Zhang, Appl. Phys. Lett. 69, 1026 (1996).
    [CrossRef]
  3. Z. Jiang and X.-C. Zhang, Appl. Phys. Lett. 72, 1945 (1998).
    [CrossRef]
  4. D. M. Mittleman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, and M. Koch, Appl. Phys. B 68, 1085 (1999).
    [CrossRef]
  5. D. M. Mittleman, S. Hunsche, L. Boivin, and M. C. Nuss, Opt. Lett. 22, 904 (1997).
    [CrossRef] [PubMed]
  6. G. T. Herman, Image Reconstruction From Projections—The Fundamentals of Computerized Tomography (Academic, New York, 1980).
  7. A. C. Kak and M. Slaney, Principles of Computerized Tomographic Imaging (Society for Industrial and Applied Mathematics, Philadelphia, Pa., 2001).
    [CrossRef]
  8. B. Ferguson, S. Wang, D. Gray, D. Abbott, and X.-C. Zhang, in Thirteenth International Conference on Ultrafast Phenomena, (Optical Society of America, Washington, D.C., 2002), pp. 450–451.

1999 (1)

D. M. Mittleman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, and M. Koch, Appl. Phys. B 68, 1085 (1999).
[CrossRef]

1998 (1)

Z. Jiang and X.-C. Zhang, Appl. Phys. Lett. 72, 1945 (1998).
[CrossRef]

1997 (1)

1996 (1)

Q. Wu, T. D. Hewitt, and X.-C. Zhang, Appl. Phys. Lett. 69, 1026 (1996).
[CrossRef]

1995 (1)

Abbott, D.

B. Ferguson, S. Wang, D. Gray, D. Abbott, and X.-C. Zhang, in Thirteenth International Conference on Ultrafast Phenomena, (Optical Society of America, Washington, D.C., 2002), pp. 450–451.

Baraniuk, R. G.

D. M. Mittleman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, and M. Koch, Appl. Phys. B 68, 1085 (1999).
[CrossRef]

Boivin, L.

Ferguson, B.

B. Ferguson, S. Wang, D. Gray, D. Abbott, and X.-C. Zhang, in Thirteenth International Conference on Ultrafast Phenomena, (Optical Society of America, Washington, D.C., 2002), pp. 450–451.

Gray, D.

B. Ferguson, S. Wang, D. Gray, D. Abbott, and X.-C. Zhang, in Thirteenth International Conference on Ultrafast Phenomena, (Optical Society of America, Washington, D.C., 2002), pp. 450–451.

Gupta, M.

D. M. Mittleman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, and M. Koch, Appl. Phys. B 68, 1085 (1999).
[CrossRef]

Herman, G. T.

G. T. Herman, Image Reconstruction From Projections—The Fundamentals of Computerized Tomography (Academic, New York, 1980).

Hewitt, T. D.

Q. Wu, T. D. Hewitt, and X.-C. Zhang, Appl. Phys. Lett. 69, 1026 (1996).
[CrossRef]

Hu, B. B.

Hunsche, S.

Jiang, Z.

Z. Jiang and X.-C. Zhang, Appl. Phys. Lett. 72, 1945 (1998).
[CrossRef]

Kak, A. C.

A. C. Kak and M. Slaney, Principles of Computerized Tomographic Imaging (Society for Industrial and Applied Mathematics, Philadelphia, Pa., 2001).
[CrossRef]

Koch, M.

D. M. Mittleman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, and M. Koch, Appl. Phys. B 68, 1085 (1999).
[CrossRef]

Mittleman, D. M.

D. M. Mittleman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, and M. Koch, Appl. Phys. B 68, 1085 (1999).
[CrossRef]

D. M. Mittleman, S. Hunsche, L. Boivin, and M. C. Nuss, Opt. Lett. 22, 904 (1997).
[CrossRef] [PubMed]

Neelamani, R.

D. M. Mittleman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, and M. Koch, Appl. Phys. B 68, 1085 (1999).
[CrossRef]

Nuss, M. C.

Rudd, J. V.

D. M. Mittleman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, and M. Koch, Appl. Phys. B 68, 1085 (1999).
[CrossRef]

Slaney, M.

A. C. Kak and M. Slaney, Principles of Computerized Tomographic Imaging (Society for Industrial and Applied Mathematics, Philadelphia, Pa., 2001).
[CrossRef]

Wang, S.

B. Ferguson, S. Wang, D. Gray, D. Abbott, and X.-C. Zhang, in Thirteenth International Conference on Ultrafast Phenomena, (Optical Society of America, Washington, D.C., 2002), pp. 450–451.

Wu, Q.

Q. Wu, T. D. Hewitt, and X.-C. Zhang, Appl. Phys. Lett. 69, 1026 (1996).
[CrossRef]

Zhang, X.-C.

Z. Jiang and X.-C. Zhang, Appl. Phys. Lett. 72, 1945 (1998).
[CrossRef]

Q. Wu, T. D. Hewitt, and X.-C. Zhang, Appl. Phys. Lett. 69, 1026 (1996).
[CrossRef]

B. Ferguson, S. Wang, D. Gray, D. Abbott, and X.-C. Zhang, in Thirteenth International Conference on Ultrafast Phenomena, (Optical Society of America, Washington, D.C., 2002), pp. 450–451.

Appl. Phys. B (1)

D. M. Mittleman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, and M. Koch, Appl. Phys. B 68, 1085 (1999).
[CrossRef]

Appl. Phys. Lett. (2)

Q. Wu, T. D. Hewitt, and X.-C. Zhang, Appl. Phys. Lett. 69, 1026 (1996).
[CrossRef]

Z. Jiang and X.-C. Zhang, Appl. Phys. Lett. 72, 1945 (1998).
[CrossRef]

Opt. Lett. (2)

Other (3)

G. T. Herman, Image Reconstruction From Projections—The Fundamentals of Computerized Tomography (Academic, New York, 1980).

A. C. Kak and M. Slaney, Principles of Computerized Tomographic Imaging (Society for Industrial and Applied Mathematics, Philadelphia, Pa., 2001).
[CrossRef]

B. Ferguson, S. Wang, D. Gray, D. Abbott, and X.-C. Zhang, in Thirteenth International Conference on Ultrafast Phenomena, (Optical Society of America, Washington, D.C., 2002), pp. 450–451.

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Figures (4)

Fig. 1
Fig. 1

Simplified hardware schematic used for T-ray CT. The ultrafast laser pulses are split into pump and probe beams. The pump beam triggers a biased (2000-V) wide-aperture antenna to generate THz pulses that are focused on the target by parabolic mirrors. The probe beam is linearly chirped by a grating pair to a pulse width of 30 ps. The THz temporal profile is encoded on the probe pulse by a 4-mm-thick ZnTe EO detector crystal and a pair of crossed polarizers. A spectrometer and a CCD camera are used to recover the THz signal. Inset, photograph of the rotation stage and sample. The sample is a dielectric sphere.

Fig. 2
Fig. 2

A vial and plastic tube were used to test the T-ray CT system. (a) Optical image of the object. The timing of the peak of the pulse in the time domain was used as the input to the filtered backprojection algorithm and the cross section was reconstructed as shown in (b). Gray-scale intensity reflects the refractive index of the sample at each pixel; darker pixels correspond to a higher refractive index.

Fig. 3
Fig. 3

A sheet of polyethylene was bent into an S shape and imaged with the T-ray CT system. (a) Optical image of the sample. The measured data were Fourier transformed, and the imaginary parts of the Fourier domain responses at four different frequencies were used to reconstruct the sample. (b) Reconstructed cross-sectional slices of the sample: (i) 0.2 THz, (ii) 0.4 THz, (iii) 0.6 THz, (iv) 0.8 THz.

Fig. 4
Fig. 4

A piece of turkey bone was imaged with the T-ray CT system. The fine structure inside the bone is of the order of the THz wavelength and therefore causes difficulties in reconstruction. (a) Optical image. The turkey bone was reconstructed, and (b) a 3D rendered image was generated. The reconstruction used the amplitude of the THz pulses at each pixel as the input to the filtered backprojection algorithm.

Equations (3)

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Pdω,θ,l=PtωexpLθ,l-iωnˆxcdx,
Sθ,ω=-sθ,lexp-i2πwldl,
nˆx,y=0π-Sθ,wwexpi2πwldwdθ.

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