Abstract

We present an imaging system designed for use in the terahertz range. As the radiation source a backward-wave oscillator was chosen for its special features such as high output power, good wave-front quality, good stability, and wavelength tunability from 520 to 710 GHz. Detection is achieved with a pyroelectric sensor operated at room temperature. The alignment procedure for the optical elements is described, and several methods to reduce the etalon effect that are inherent in monochromatic sources are discussed. The terahertz spot size in the sample plane is 550 μm (nearly the diffraction limit), and the signal-to-noise ratio is 10,000:1; other characteristics were also measured and are presented in detail. A number of preliminary applications are also shown that cover various areas: nondestructive real-time testing for plastic tubes and packaging seals; biological terahertz imaging of fresh, frozen, or freeze-dried samples; paraffin-embedded specimens of cancer tissue; and measurement of the absorption coefficient of water by use of a wedge-shaped cell.

© 2004 Optical Society of America

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  1. See, for example, Eleventh International Conference on Terahertz Electronics, J. Nishizawa, K. Hiromasa, H. Ito, eds. (IEEE, Piscataway, N.J., 2003).
  2. Y. Watanabe, K. Kawase, T. Ikari, H. Ito, Y. Ishikawa, H. Minamide, “Component spatial pattern analysis of chemicals using terahertz spectroscopic imaging,” Appl. Phys. Lett. 83, 800–802 (2003).
    [CrossRef]
  3. K. Kawase, Y. Ogawa, Y. Watanabe, “Non-destructive terahertz imaging of illicit drugs using spectral fingerprints,” Opt. Express11, 2549–2554 (2003), http://www.opticsexpress.org .
    [CrossRef]
  4. X.-C. Zhang, “Terahertz wave imaging: horizons and hurdles,” Phys. Med. Biol. 47, 3667–3677 (2002).
    [CrossRef] [PubMed]
  5. T. S. Hartwick, D. T. Hodges, D. H. Barker, F. B. Foote, “Far infrared imagery,” Appl. Opt. 15, 1919–1922 (1976).
    [CrossRef] [PubMed]
  6. B. B. Hu, M. C. Nuss, “Imaging with terahertz waves,” Opt. Lett. 20, 1716–1718 (1995).
    [CrossRef] [PubMed]
  7. K. J. Siebert, H. Quast, R. Leonhardt, T. Löffler, M. Thomson, T. Bauer, H. G. Roskos, S. Czasch, “Continuous-wave all-optoelectronic terahertz imaging,” Appl. Phys. Lett. 80, 3003–3005 (2002).
    [CrossRef]
  8. D. M. Mittelman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, M. Koch, “Recent advances in terahertz imaging,” Appl. Phys. B 68, 1085–1094 (1999).
    [CrossRef]
  9. T. Bauer, J. S. Kolb, T. Löffler, E. Mohler, H. G. Roskos, U. C. Pernisz, “Indium-tin-oxide-coated glass as a dichroic mirror for far-infrared electromagnetic radiation,” J. Appl. Phys. 92, 2210–2212 (2002).
    [CrossRef]
  10. P. H. Siegel, Submillimeter Wave Advanced Technology, Jet Propulsion Laboratory, California Institute of Technology, Mail Code 168-314, 4800 Oak Grove Drive, Pasadena, Calif. 91109 (personal communication, December2003).
  11. K. Kawase, J. Shikata, H. Ito, “Terahertz wave parametric source,” J. Phys. D 34, R1–R14 (2001).
  12. O. A. Simpson, B. L. Bean, S. Perkowitz, “Far infrared optical constants of liquid water measured with an optically pumped laser,” J. Opt. Soc. Am. 69, 1723–1726 (1979).
    [CrossRef]
  13. D. M. Wieliczka, S. Weng, M. R. Querry, “Wedge shaped cell for highly absorbent liquids: infrared optical constants of water,” Appl. Opt. 28, 1714–1719 (1989).
    [CrossRef] [PubMed]
  14. M. R. Querry, D. M. Wieliczka, D. J. Segelstein, “Water (H2O),” in Handbook of Optical Constants of Solids II, E. D. Palik, ed. (Academic, San Diego, Calif., 1991), pp. 1059–1077.
  15. S. Hadjiloucas, L. S. Karatzas, J. W. Bowen, “Measurement of leaf water content using terahertz radiation,” IEEE Trans. Microwave Theory Tech. 47, 142–149 (1999).
    [CrossRef]
  16. K. J. Siebert, T. Löffler, H. Quast, M. Thomson, T. Bauer, R. Leonhardt, S. Czasch, H. G. Roskos, “All-optoelectronic continuous wave THz imaging for biomedical applications,” Phys. Med. Biol. 47, 3743–3748 (2002).
    [CrossRef] [PubMed]
  17. T. Löffler, T. Bauer, K. J. Siebert, H. G. Roskos, A. Fitzgerald, S. Czasch, “Terahertz dark-field imaging of biomedical tissue,” Opt. Express9, 616–621 (2001), http://www.opticsexpress.org .
  18. J. Nishizawa, “Exploring the terahertz range,” J. Acoust. Soc. Jpn. 57, 163–169 (2001).
  19. P. Knobloch, C. Schildknecht, T. Kleine-Ostmann, M. Koch, S. Hoffmann, M. Hofmann, E. Rehberg, M. Sperling, K. Donhuijsen, G. Hein, K. Pierz, “Medical THz imaging: an investigation of histo-pathological samples,” Phys. Med. Biol. 47, 3875–3884 (2002).
    [CrossRef] [PubMed]
  20. T. Löffler, K. Siebert, S. Czasch, T. Bauer, H. G. Roskos, “Visualization and classification in biomedical terahertz pulsed imaging,” Phys. Med. Biol. 47, 3847–3852 (2002).
    [CrossRef] [PubMed]

2003

Y. Watanabe, K. Kawase, T. Ikari, H. Ito, Y. Ishikawa, H. Minamide, “Component spatial pattern analysis of chemicals using terahertz spectroscopic imaging,” Appl. Phys. Lett. 83, 800–802 (2003).
[CrossRef]

2002

X.-C. Zhang, “Terahertz wave imaging: horizons and hurdles,” Phys. Med. Biol. 47, 3667–3677 (2002).
[CrossRef] [PubMed]

K. J. Siebert, H. Quast, R. Leonhardt, T. Löffler, M. Thomson, T. Bauer, H. G. Roskos, S. Czasch, “Continuous-wave all-optoelectronic terahertz imaging,” Appl. Phys. Lett. 80, 3003–3005 (2002).
[CrossRef]

T. Bauer, J. S. Kolb, T. Löffler, E. Mohler, H. G. Roskos, U. C. Pernisz, “Indium-tin-oxide-coated glass as a dichroic mirror for far-infrared electromagnetic radiation,” J. Appl. Phys. 92, 2210–2212 (2002).
[CrossRef]

K. J. Siebert, T. Löffler, H. Quast, M. Thomson, T. Bauer, R. Leonhardt, S. Czasch, H. G. Roskos, “All-optoelectronic continuous wave THz imaging for biomedical applications,” Phys. Med. Biol. 47, 3743–3748 (2002).
[CrossRef] [PubMed]

P. Knobloch, C. Schildknecht, T. Kleine-Ostmann, M. Koch, S. Hoffmann, M. Hofmann, E. Rehberg, M. Sperling, K. Donhuijsen, G. Hein, K. Pierz, “Medical THz imaging: an investigation of histo-pathological samples,” Phys. Med. Biol. 47, 3875–3884 (2002).
[CrossRef] [PubMed]

T. Löffler, K. Siebert, S. Czasch, T. Bauer, H. G. Roskos, “Visualization and classification in biomedical terahertz pulsed imaging,” Phys. Med. Biol. 47, 3847–3852 (2002).
[CrossRef] [PubMed]

2001

J. Nishizawa, “Exploring the terahertz range,” J. Acoust. Soc. Jpn. 57, 163–169 (2001).

K. Kawase, J. Shikata, H. Ito, “Terahertz wave parametric source,” J. Phys. D 34, R1–R14 (2001).

1999

D. M. Mittelman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, M. Koch, “Recent advances in terahertz imaging,” Appl. Phys. B 68, 1085–1094 (1999).
[CrossRef]

S. Hadjiloucas, L. S. Karatzas, J. W. Bowen, “Measurement of leaf water content using terahertz radiation,” IEEE Trans. Microwave Theory Tech. 47, 142–149 (1999).
[CrossRef]

1995

1989

1979

1976

Baraniuk, R. G.

D. M. Mittelman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, M. Koch, “Recent advances in terahertz imaging,” Appl. Phys. B 68, 1085–1094 (1999).
[CrossRef]

Barker, D. H.

Bauer, T.

K. J. Siebert, H. Quast, R. Leonhardt, T. Löffler, M. Thomson, T. Bauer, H. G. Roskos, S. Czasch, “Continuous-wave all-optoelectronic terahertz imaging,” Appl. Phys. Lett. 80, 3003–3005 (2002).
[CrossRef]

T. Bauer, J. S. Kolb, T. Löffler, E. Mohler, H. G. Roskos, U. C. Pernisz, “Indium-tin-oxide-coated glass as a dichroic mirror for far-infrared electromagnetic radiation,” J. Appl. Phys. 92, 2210–2212 (2002).
[CrossRef]

K. J. Siebert, T. Löffler, H. Quast, M. Thomson, T. Bauer, R. Leonhardt, S. Czasch, H. G. Roskos, “All-optoelectronic continuous wave THz imaging for biomedical applications,” Phys. Med. Biol. 47, 3743–3748 (2002).
[CrossRef] [PubMed]

T. Löffler, K. Siebert, S. Czasch, T. Bauer, H. G. Roskos, “Visualization and classification in biomedical terahertz pulsed imaging,” Phys. Med. Biol. 47, 3847–3852 (2002).
[CrossRef] [PubMed]

Bean, B. L.

Bowen, J. W.

S. Hadjiloucas, L. S. Karatzas, J. W. Bowen, “Measurement of leaf water content using terahertz radiation,” IEEE Trans. Microwave Theory Tech. 47, 142–149 (1999).
[CrossRef]

Czasch, S.

K. J. Siebert, T. Löffler, H. Quast, M. Thomson, T. Bauer, R. Leonhardt, S. Czasch, H. G. Roskos, “All-optoelectronic continuous wave THz imaging for biomedical applications,” Phys. Med. Biol. 47, 3743–3748 (2002).
[CrossRef] [PubMed]

T. Löffler, K. Siebert, S. Czasch, T. Bauer, H. G. Roskos, “Visualization and classification in biomedical terahertz pulsed imaging,” Phys. Med. Biol. 47, 3847–3852 (2002).
[CrossRef] [PubMed]

K. J. Siebert, H. Quast, R. Leonhardt, T. Löffler, M. Thomson, T. Bauer, H. G. Roskos, S. Czasch, “Continuous-wave all-optoelectronic terahertz imaging,” Appl. Phys. Lett. 80, 3003–3005 (2002).
[CrossRef]

Donhuijsen, K.

P. Knobloch, C. Schildknecht, T. Kleine-Ostmann, M. Koch, S. Hoffmann, M. Hofmann, E. Rehberg, M. Sperling, K. Donhuijsen, G. Hein, K. Pierz, “Medical THz imaging: an investigation of histo-pathological samples,” Phys. Med. Biol. 47, 3875–3884 (2002).
[CrossRef] [PubMed]

Foote, F. B.

Gupta, M.

D. M. Mittelman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, M. Koch, “Recent advances in terahertz imaging,” Appl. Phys. B 68, 1085–1094 (1999).
[CrossRef]

Hadjiloucas, S.

S. Hadjiloucas, L. S. Karatzas, J. W. Bowen, “Measurement of leaf water content using terahertz radiation,” IEEE Trans. Microwave Theory Tech. 47, 142–149 (1999).
[CrossRef]

Hartwick, T. S.

Hein, G.

P. Knobloch, C. Schildknecht, T. Kleine-Ostmann, M. Koch, S. Hoffmann, M. Hofmann, E. Rehberg, M. Sperling, K. Donhuijsen, G. Hein, K. Pierz, “Medical THz imaging: an investigation of histo-pathological samples,” Phys. Med. Biol. 47, 3875–3884 (2002).
[CrossRef] [PubMed]

Hodges, D. T.

Hoffmann, S.

P. Knobloch, C. Schildknecht, T. Kleine-Ostmann, M. Koch, S. Hoffmann, M. Hofmann, E. Rehberg, M. Sperling, K. Donhuijsen, G. Hein, K. Pierz, “Medical THz imaging: an investigation of histo-pathological samples,” Phys. Med. Biol. 47, 3875–3884 (2002).
[CrossRef] [PubMed]

Hofmann, M.

P. Knobloch, C. Schildknecht, T. Kleine-Ostmann, M. Koch, S. Hoffmann, M. Hofmann, E. Rehberg, M. Sperling, K. Donhuijsen, G. Hein, K. Pierz, “Medical THz imaging: an investigation of histo-pathological samples,” Phys. Med. Biol. 47, 3875–3884 (2002).
[CrossRef] [PubMed]

Hu, B. B.

Ikari, T.

Y. Watanabe, K. Kawase, T. Ikari, H. Ito, Y. Ishikawa, H. Minamide, “Component spatial pattern analysis of chemicals using terahertz spectroscopic imaging,” Appl. Phys. Lett. 83, 800–802 (2003).
[CrossRef]

Ishikawa, Y.

Y. Watanabe, K. Kawase, T. Ikari, H. Ito, Y. Ishikawa, H. Minamide, “Component spatial pattern analysis of chemicals using terahertz spectroscopic imaging,” Appl. Phys. Lett. 83, 800–802 (2003).
[CrossRef]

Ito, H.

Y. Watanabe, K. Kawase, T. Ikari, H. Ito, Y. Ishikawa, H. Minamide, “Component spatial pattern analysis of chemicals using terahertz spectroscopic imaging,” Appl. Phys. Lett. 83, 800–802 (2003).
[CrossRef]

K. Kawase, J. Shikata, H. Ito, “Terahertz wave parametric source,” J. Phys. D 34, R1–R14 (2001).

Karatzas, L. S.

S. Hadjiloucas, L. S. Karatzas, J. W. Bowen, “Measurement of leaf water content using terahertz radiation,” IEEE Trans. Microwave Theory Tech. 47, 142–149 (1999).
[CrossRef]

Kawase, K.

Y. Watanabe, K. Kawase, T. Ikari, H. Ito, Y. Ishikawa, H. Minamide, “Component spatial pattern analysis of chemicals using terahertz spectroscopic imaging,” Appl. Phys. Lett. 83, 800–802 (2003).
[CrossRef]

K. Kawase, J. Shikata, H. Ito, “Terahertz wave parametric source,” J. Phys. D 34, R1–R14 (2001).

Kleine-Ostmann, T.

P. Knobloch, C. Schildknecht, T. Kleine-Ostmann, M. Koch, S. Hoffmann, M. Hofmann, E. Rehberg, M. Sperling, K. Donhuijsen, G. Hein, K. Pierz, “Medical THz imaging: an investigation of histo-pathological samples,” Phys. Med. Biol. 47, 3875–3884 (2002).
[CrossRef] [PubMed]

Knobloch, P.

P. Knobloch, C. Schildknecht, T. Kleine-Ostmann, M. Koch, S. Hoffmann, M. Hofmann, E. Rehberg, M. Sperling, K. Donhuijsen, G. Hein, K. Pierz, “Medical THz imaging: an investigation of histo-pathological samples,” Phys. Med. Biol. 47, 3875–3884 (2002).
[CrossRef] [PubMed]

Koch, M.

P. Knobloch, C. Schildknecht, T. Kleine-Ostmann, M. Koch, S. Hoffmann, M. Hofmann, E. Rehberg, M. Sperling, K. Donhuijsen, G. Hein, K. Pierz, “Medical THz imaging: an investigation of histo-pathological samples,” Phys. Med. Biol. 47, 3875–3884 (2002).
[CrossRef] [PubMed]

D. M. Mittelman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, M. Koch, “Recent advances in terahertz imaging,” Appl. Phys. B 68, 1085–1094 (1999).
[CrossRef]

Kolb, J. S.

T. Bauer, J. S. Kolb, T. Löffler, E. Mohler, H. G. Roskos, U. C. Pernisz, “Indium-tin-oxide-coated glass as a dichroic mirror for far-infrared electromagnetic radiation,” J. Appl. Phys. 92, 2210–2212 (2002).
[CrossRef]

Leonhardt, R.

K. J. Siebert, H. Quast, R. Leonhardt, T. Löffler, M. Thomson, T. Bauer, H. G. Roskos, S. Czasch, “Continuous-wave all-optoelectronic terahertz imaging,” Appl. Phys. Lett. 80, 3003–3005 (2002).
[CrossRef]

K. J. Siebert, T. Löffler, H. Quast, M. Thomson, T. Bauer, R. Leonhardt, S. Czasch, H. G. Roskos, “All-optoelectronic continuous wave THz imaging for biomedical applications,” Phys. Med. Biol. 47, 3743–3748 (2002).
[CrossRef] [PubMed]

Löffler, T.

K. J. Siebert, T. Löffler, H. Quast, M. Thomson, T. Bauer, R. Leonhardt, S. Czasch, H. G. Roskos, “All-optoelectronic continuous wave THz imaging for biomedical applications,” Phys. Med. Biol. 47, 3743–3748 (2002).
[CrossRef] [PubMed]

T. Löffler, K. Siebert, S. Czasch, T. Bauer, H. G. Roskos, “Visualization and classification in biomedical terahertz pulsed imaging,” Phys. Med. Biol. 47, 3847–3852 (2002).
[CrossRef] [PubMed]

K. J. Siebert, H. Quast, R. Leonhardt, T. Löffler, M. Thomson, T. Bauer, H. G. Roskos, S. Czasch, “Continuous-wave all-optoelectronic terahertz imaging,” Appl. Phys. Lett. 80, 3003–3005 (2002).
[CrossRef]

T. Bauer, J. S. Kolb, T. Löffler, E. Mohler, H. G. Roskos, U. C. Pernisz, “Indium-tin-oxide-coated glass as a dichroic mirror for far-infrared electromagnetic radiation,” J. Appl. Phys. 92, 2210–2212 (2002).
[CrossRef]

Minamide, H.

Y. Watanabe, K. Kawase, T. Ikari, H. Ito, Y. Ishikawa, H. Minamide, “Component spatial pattern analysis of chemicals using terahertz spectroscopic imaging,” Appl. Phys. Lett. 83, 800–802 (2003).
[CrossRef]

Mittelman, D. M.

D. M. Mittelman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, M. Koch, “Recent advances in terahertz imaging,” Appl. Phys. B 68, 1085–1094 (1999).
[CrossRef]

Mohler, E.

T. Bauer, J. S. Kolb, T. Löffler, E. Mohler, H. G. Roskos, U. C. Pernisz, “Indium-tin-oxide-coated glass as a dichroic mirror for far-infrared electromagnetic radiation,” J. Appl. Phys. 92, 2210–2212 (2002).
[CrossRef]

Neelamani, R.

D. M. Mittelman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, M. Koch, “Recent advances in terahertz imaging,” Appl. Phys. B 68, 1085–1094 (1999).
[CrossRef]

Nishizawa, J.

J. Nishizawa, “Exploring the terahertz range,” J. Acoust. Soc. Jpn. 57, 163–169 (2001).

Nuss, M. C.

Perkowitz, S.

Pernisz, U. C.

T. Bauer, J. S. Kolb, T. Löffler, E. Mohler, H. G. Roskos, U. C. Pernisz, “Indium-tin-oxide-coated glass as a dichroic mirror for far-infrared electromagnetic radiation,” J. Appl. Phys. 92, 2210–2212 (2002).
[CrossRef]

Pierz, K.

P. Knobloch, C. Schildknecht, T. Kleine-Ostmann, M. Koch, S. Hoffmann, M. Hofmann, E. Rehberg, M. Sperling, K. Donhuijsen, G. Hein, K. Pierz, “Medical THz imaging: an investigation of histo-pathological samples,” Phys. Med. Biol. 47, 3875–3884 (2002).
[CrossRef] [PubMed]

Quast, H.

K. J. Siebert, T. Löffler, H. Quast, M. Thomson, T. Bauer, R. Leonhardt, S. Czasch, H. G. Roskos, “All-optoelectronic continuous wave THz imaging for biomedical applications,” Phys. Med. Biol. 47, 3743–3748 (2002).
[CrossRef] [PubMed]

K. J. Siebert, H. Quast, R. Leonhardt, T. Löffler, M. Thomson, T. Bauer, H. G. Roskos, S. Czasch, “Continuous-wave all-optoelectronic terahertz imaging,” Appl. Phys. Lett. 80, 3003–3005 (2002).
[CrossRef]

Querry, M. R.

D. M. Wieliczka, S. Weng, M. R. Querry, “Wedge shaped cell for highly absorbent liquids: infrared optical constants of water,” Appl. Opt. 28, 1714–1719 (1989).
[CrossRef] [PubMed]

M. R. Querry, D. M. Wieliczka, D. J. Segelstein, “Water (H2O),” in Handbook of Optical Constants of Solids II, E. D. Palik, ed. (Academic, San Diego, Calif., 1991), pp. 1059–1077.

Rehberg, E.

P. Knobloch, C. Schildknecht, T. Kleine-Ostmann, M. Koch, S. Hoffmann, M. Hofmann, E. Rehberg, M. Sperling, K. Donhuijsen, G. Hein, K. Pierz, “Medical THz imaging: an investigation of histo-pathological samples,” Phys. Med. Biol. 47, 3875–3884 (2002).
[CrossRef] [PubMed]

Roskos, H. G.

K. J. Siebert, T. Löffler, H. Quast, M. Thomson, T. Bauer, R. Leonhardt, S. Czasch, H. G. Roskos, “All-optoelectronic continuous wave THz imaging for biomedical applications,” Phys. Med. Biol. 47, 3743–3748 (2002).
[CrossRef] [PubMed]

T. Bauer, J. S. Kolb, T. Löffler, E. Mohler, H. G. Roskos, U. C. Pernisz, “Indium-tin-oxide-coated glass as a dichroic mirror for far-infrared electromagnetic radiation,” J. Appl. Phys. 92, 2210–2212 (2002).
[CrossRef]

K. J. Siebert, H. Quast, R. Leonhardt, T. Löffler, M. Thomson, T. Bauer, H. G. Roskos, S. Czasch, “Continuous-wave all-optoelectronic terahertz imaging,” Appl. Phys. Lett. 80, 3003–3005 (2002).
[CrossRef]

T. Löffler, K. Siebert, S. Czasch, T. Bauer, H. G. Roskos, “Visualization and classification in biomedical terahertz pulsed imaging,” Phys. Med. Biol. 47, 3847–3852 (2002).
[CrossRef] [PubMed]

Rudd, J. V.

D. M. Mittelman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, M. Koch, “Recent advances in terahertz imaging,” Appl. Phys. B 68, 1085–1094 (1999).
[CrossRef]

Schildknecht, C.

P. Knobloch, C. Schildknecht, T. Kleine-Ostmann, M. Koch, S. Hoffmann, M. Hofmann, E. Rehberg, M. Sperling, K. Donhuijsen, G. Hein, K. Pierz, “Medical THz imaging: an investigation of histo-pathological samples,” Phys. Med. Biol. 47, 3875–3884 (2002).
[CrossRef] [PubMed]

Segelstein, D. J.

M. R. Querry, D. M. Wieliczka, D. J. Segelstein, “Water (H2O),” in Handbook of Optical Constants of Solids II, E. D. Palik, ed. (Academic, San Diego, Calif., 1991), pp. 1059–1077.

Shikata, J.

K. Kawase, J. Shikata, H. Ito, “Terahertz wave parametric source,” J. Phys. D 34, R1–R14 (2001).

Siebert, K.

T. Löffler, K. Siebert, S. Czasch, T. Bauer, H. G. Roskos, “Visualization and classification in biomedical terahertz pulsed imaging,” Phys. Med. Biol. 47, 3847–3852 (2002).
[CrossRef] [PubMed]

Siebert, K. J.

K. J. Siebert, T. Löffler, H. Quast, M. Thomson, T. Bauer, R. Leonhardt, S. Czasch, H. G. Roskos, “All-optoelectronic continuous wave THz imaging for biomedical applications,” Phys. Med. Biol. 47, 3743–3748 (2002).
[CrossRef] [PubMed]

K. J. Siebert, H. Quast, R. Leonhardt, T. Löffler, M. Thomson, T. Bauer, H. G. Roskos, S. Czasch, “Continuous-wave all-optoelectronic terahertz imaging,” Appl. Phys. Lett. 80, 3003–3005 (2002).
[CrossRef]

Siegel, P. H.

P. H. Siegel, Submillimeter Wave Advanced Technology, Jet Propulsion Laboratory, California Institute of Technology, Mail Code 168-314, 4800 Oak Grove Drive, Pasadena, Calif. 91109 (personal communication, December2003).

Simpson, O. A.

Sperling, M.

P. Knobloch, C. Schildknecht, T. Kleine-Ostmann, M. Koch, S. Hoffmann, M. Hofmann, E. Rehberg, M. Sperling, K. Donhuijsen, G. Hein, K. Pierz, “Medical THz imaging: an investigation of histo-pathological samples,” Phys. Med. Biol. 47, 3875–3884 (2002).
[CrossRef] [PubMed]

Thomson, M.

K. J. Siebert, T. Löffler, H. Quast, M. Thomson, T. Bauer, R. Leonhardt, S. Czasch, H. G. Roskos, “All-optoelectronic continuous wave THz imaging for biomedical applications,” Phys. Med. Biol. 47, 3743–3748 (2002).
[CrossRef] [PubMed]

K. J. Siebert, H. Quast, R. Leonhardt, T. Löffler, M. Thomson, T. Bauer, H. G. Roskos, S. Czasch, “Continuous-wave all-optoelectronic terahertz imaging,” Appl. Phys. Lett. 80, 3003–3005 (2002).
[CrossRef]

Watanabe, Y.

Y. Watanabe, K. Kawase, T. Ikari, H. Ito, Y. Ishikawa, H. Minamide, “Component spatial pattern analysis of chemicals using terahertz spectroscopic imaging,” Appl. Phys. Lett. 83, 800–802 (2003).
[CrossRef]

Weng, S.

Wieliczka, D. M.

D. M. Wieliczka, S. Weng, M. R. Querry, “Wedge shaped cell for highly absorbent liquids: infrared optical constants of water,” Appl. Opt. 28, 1714–1719 (1989).
[CrossRef] [PubMed]

M. R. Querry, D. M. Wieliczka, D. J. Segelstein, “Water (H2O),” in Handbook of Optical Constants of Solids II, E. D. Palik, ed. (Academic, San Diego, Calif., 1991), pp. 1059–1077.

Zhang, X.-C.

X.-C. Zhang, “Terahertz wave imaging: horizons and hurdles,” Phys. Med. Biol. 47, 3667–3677 (2002).
[CrossRef] [PubMed]

Appl. Opt.

Appl. Phys. B

D. M. Mittelman, M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd, M. Koch, “Recent advances in terahertz imaging,” Appl. Phys. B 68, 1085–1094 (1999).
[CrossRef]

Appl. Phys. Lett.

Y. Watanabe, K. Kawase, T. Ikari, H. Ito, Y. Ishikawa, H. Minamide, “Component spatial pattern analysis of chemicals using terahertz spectroscopic imaging,” Appl. Phys. Lett. 83, 800–802 (2003).
[CrossRef]

K. J. Siebert, H. Quast, R. Leonhardt, T. Löffler, M. Thomson, T. Bauer, H. G. Roskos, S. Czasch, “Continuous-wave all-optoelectronic terahertz imaging,” Appl. Phys. Lett. 80, 3003–3005 (2002).
[CrossRef]

IEEE Trans. Microwave Theory Tech.

S. Hadjiloucas, L. S. Karatzas, J. W. Bowen, “Measurement of leaf water content using terahertz radiation,” IEEE Trans. Microwave Theory Tech. 47, 142–149 (1999).
[CrossRef]

J. Acoust. Soc. Jpn.

J. Nishizawa, “Exploring the terahertz range,” J. Acoust. Soc. Jpn. 57, 163–169 (2001).

J. Appl. Phys.

T. Bauer, J. S. Kolb, T. Löffler, E. Mohler, H. G. Roskos, U. C. Pernisz, “Indium-tin-oxide-coated glass as a dichroic mirror for far-infrared electromagnetic radiation,” J. Appl. Phys. 92, 2210–2212 (2002).
[CrossRef]

J. Opt. Soc. Am.

J. Phys. D

K. Kawase, J. Shikata, H. Ito, “Terahertz wave parametric source,” J. Phys. D 34, R1–R14 (2001).

Opt. Lett.

Phys. Med. Biol.

X.-C. Zhang, “Terahertz wave imaging: horizons and hurdles,” Phys. Med. Biol. 47, 3667–3677 (2002).
[CrossRef] [PubMed]

P. Knobloch, C. Schildknecht, T. Kleine-Ostmann, M. Koch, S. Hoffmann, M. Hofmann, E. Rehberg, M. Sperling, K. Donhuijsen, G. Hein, K. Pierz, “Medical THz imaging: an investigation of histo-pathological samples,” Phys. Med. Biol. 47, 3875–3884 (2002).
[CrossRef] [PubMed]

T. Löffler, K. Siebert, S. Czasch, T. Bauer, H. G. Roskos, “Visualization and classification in biomedical terahertz pulsed imaging,” Phys. Med. Biol. 47, 3847–3852 (2002).
[CrossRef] [PubMed]

K. J. Siebert, T. Löffler, H. Quast, M. Thomson, T. Bauer, R. Leonhardt, S. Czasch, H. G. Roskos, “All-optoelectronic continuous wave THz imaging for biomedical applications,” Phys. Med. Biol. 47, 3743–3748 (2002).
[CrossRef] [PubMed]

Other

T. Löffler, T. Bauer, K. J. Siebert, H. G. Roskos, A. Fitzgerald, S. Czasch, “Terahertz dark-field imaging of biomedical tissue,” Opt. Express9, 616–621 (2001), http://www.opticsexpress.org .

M. R. Querry, D. M. Wieliczka, D. J. Segelstein, “Water (H2O),” in Handbook of Optical Constants of Solids II, E. D. Palik, ed. (Academic, San Diego, Calif., 1991), pp. 1059–1077.

See, for example, Eleventh International Conference on Terahertz Electronics, J. Nishizawa, K. Hiromasa, H. Ito, eds. (IEEE, Piscataway, N.J., 2003).

K. Kawase, Y. Ogawa, Y. Watanabe, “Non-destructive terahertz imaging of illicit drugs using spectral fingerprints,” Opt. Express11, 2549–2554 (2003), http://www.opticsexpress.org .
[CrossRef]

P. H. Siegel, Submillimeter Wave Advanced Technology, Jet Propulsion Laboratory, California Institute of Technology, Mail Code 168-314, 4800 Oak Grove Drive, Pasadena, Calif. 91109 (personal communication, December2003).

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Figures (16)

Fig. 1
Fig. 1

Schematic of the imaging system. The numbers on the parabolic mirrors represent their effective reflected focal lengths in millimeters; all four mirrors are 76.2 mm in diameter.

Fig. 2
Fig. 2

Spectral characteristics of the BWO output obtained by scanning the voltage applied to its tube. The periodic variations in the spectrum correspond to an etalon effect inside the source.

Fig. 3
Fig. 3

Reduction of the etalon effect by tilting the sample. (a) The first scan is made in the normal horizontal position, and the resultant image exhibits fringes as indicated by arrows. (b) For the second scan the sample was tilted at a 27° angle. The visibility of the interference fringes was clearly reduced.

Fig. 4
Fig. 4

Reduction of the etalon effect by modulation of the BWO wave frequency. (a) The image of a polystyrene plate scanned without any modulation exhibits intense interference fringes. (b) The same sample was scanned while frequency modulation was applied with increasing amplitude from left to right. The fringe visibility fell to local minima, indicated by arrows, corresponding to spectral widths of 0.14 and 0.65 GHz. The contrast was amplified—to the same extent in both images—for clarity; the actual images are shown as insets.

Fig. 5
Fig. 5

Measurement of the focal spot size by the knife-edge method. The measured signal (gray dots) was fitted with an error function. When the knife is tangent to the circle at half the Gaussian bell height, the transmitted signal is 11.9% or 88.1% of the full signal; these levels are shown by the two horizontal lines.

Fig. 6
Fig. 6

Images of a 0.5-mm hole in aluminum foil. The number on each picture represents the BWO wave frequency in gigahertz. A length of 1 mm is shown as a white bar above each spot. As the images were all scanned at the same speed, low output levels produced noisier signals.

Fig. 7
Fig. 7

(a) The BWO output power varies in time by ±2% over a 0.5-h interval. More information is obtained by Fourier processing of this variation, which shows typical behavior for Brownian noise (b). The frequency dimension was expressed as time scale by simple inversion for ease of understanding.

Fig. 8
Fig. 8

Comparison of three THz imaging systems. The ability to resolve the metallic lines in this sample and the uniformity of the brighter areas indicate the advantages offered by the BWO system in terms of resolution and noise level. The TPO image was recorded at 1.5 THz; the TDS and BWO images were both recorded at 0.59 THz. The scanning steps were small enough not to limit the resolving power. The size of the imaged area is 10 mm × 10 mm.

Fig. 9
Fig. 9

(a) Metallic objects—a 5-yen coin, a screw, and a paper clip—inserted in a cardboard box are revealed by THz imaging. (b) The shape of the RIKEN logo was cut from aluminum foil and imaged through an 18-mm-thick block of Teflon.

Fig. 10
Fig. 10

THz image of a railway payment card. The large loop made from six thin wires is the antenna that allows the card to be used just by being placed near the reading-writing machine. Other elements of the circuitry can be seen.

Fig. 11
Fig. 11

(a) Polyurethane tube with a defect. (b) Schematic of an optical adapter for probing the plastic tube from several directions simultaneously. The THz beam enters and exits as indicated by the arrows and is reflected by mirrors.

Fig. 12
Fig. 12

Defect in polyethylene packaging seals. The peak at the middle is produced by a water-filled channel, 30 μm in diameter. The peak shape comes from the fact that only the ac component of the signal, in a selected frequency band, is measured.

Fig. 13
Fig. 13

Water absorption measured by the wedge-shaped cell technique. Measured data are shown as dots, and the continuous curve is the exponential decay fit. The dip at left is the shadow of the upper slide edge, corresponding to zero thickness. At the thinner part of the wedge the etalon effect inside the water can be seen as a slight waviness of the measured data. In this semilogarithmic representation the data should lie in a straight line. However, a small additive offset makes the data curve upward at the thicker end; this offset was included as an additional parameter in the fitting function.

Fig. 14
Fig. 14

The vessel structure in this freshly cut leaf could be clearly imaged. The details allowed by the 550-μm spot size are preserved by a 200-μm scanning step. The transmission of the leaf in the spaces between vessels is ∼15%.

Fig. 15
Fig. 15

THz images of biological samples. The problem of high absorption in water was solved by (a) freezing or (b)–(d) freeze drying the samples. For the frozen sample hardly any detail can be seen, although the ice does transmit much better than water. In comparison, the freeze-dried samples show clear structural details and tissue texture. The images correspond to (a) a pig tongue; (b) a chicken heart (1, right ventricle; 2, interventricular septum; 3, left ventricle); (c) a pig tongue similar to the first sample but flipped over and rotated; and (d) the cervical canal of a pig uterus (1, the myometrium; 2, the uterine cavity; 3, the endometrium).

Fig. 16
Fig. 16

Paraffin-embedded tissue samples. A liver-cancer sample was scanned at several wavelengths; we show here the results at (a) 567 GHz and (b) 676 GHz. The cancerous areas, indicated by arrows, have higher THz transmission and appear brighter. For the breast cancer sample in (c) the diseased area is indicated by the dotted, curved line at the left. Its brightness and texture are different from those of the rest of the sample.

Equations (4)

Equations on this page are rendered with MathJax. Learn more.

Ix=I0121+erf2ln 2x-xcd,
d=λfd02 ln 2π,
Δz=dmin2λπln 2,
Ix=I0 exp-αθx,

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