Proximate Imaging

Most of the work above focused on at least modest stand-off distances (> 1 m) with macroscopic object sizes (≥ 1 m). In addition, many proximate images have been made, often with THz-TDS systems [1].

In a typical experiment the target is placed at the focus of a pair of small f-value off-axis parabaloids that focus the radiation on a small point and collect the transmitted radiation. The sample is then raster scanned to produce an image. A particularly interesting example, perhaps the first made with THz-TDS methods, uses a leaf to show the migration of water as the leaf dries [1].

In a very different application SMM/THz imaging has been used in the study of art and archaeological objects [4]. Since many of these objects are layered and have relatively large transmission, this appears be a particularly good application of THz-TDS techniques.

The interest reader is referred to an extensive literature on this subject [5].

References

  1. Hu, B. B. & Nuss, M. C. Imaging with terahertz waves Opt. Lett. 20, 1716-1718 (1995). Google Scholar
  2. Grossman, E. N., Luukanen, A. & Miller, A. J. Terahertz Active Direct Detection Imagers Terahertz for Millitary and Security Applications II 5411, (2004). Google Scholar
  3. Dobroiu, A., Yamashita, M., Ohshima, Y. N., Morita, Y., Otani, C. & Kawase, K. Terahertz imaging system based on a backward-wave oscillator Appl. Opt. 43, 5637-5646 (2004). Google Scholar
  4. Jackson, J. B., Bowen, J., Walker, G., Labaune, J., Mourou, G., Menu, M. & Fukunaga, K. A survey of Terahertz Applications in Cultural Heritage Conservation Science IEEE Trans. Terahertz Sci. Technol. 1, 229-231 (2011). Google Scholar
  5. Hunsche, S., Kochb, M., Brenerc, I. & Nuss, M. C. THz near-field imaging Opt. Commun. 150, 22-26 (1998). Google Scholar
  6. Wu, Q., Hewitt, T. D. & Zhang, X. C. Two-dimensional electro-optic imaging of THz beams Appl. Phys. Lett. 69, 1026-1028 (1996). Google Scholar
  7. Zhang, X. C. Terahertz wave imaging: horizons and hurdles Phys. Med. Biol. 47, 3667-3677 (2002). Google Scholar
  8. Ajito, K. & Ueno, Y. THz Chemical Imaging for Biological Applications IEEE Trans. Terahertz Sci. Technol. 1, 293-300 (2011). Google Scholar