Abstract

Active imaging can provide significantly larger signal margins in the millimeter-wave spectral region than passive imaging, especially indoors—an important application for which there is no cold sky illumination. However, coherent effects, such as speckle, negate much of this advantage by destroying image clarity and target recognition. Moreover, active imaging demonstrations often use strategically chosen target orientations to optimally reflect power from the active illuminator back to the imaging receiver. In this paper we will discuss and show experimental results for a new active imaging approach that largely eliminates coherent effects and the need for optimized target orientation. The work described uses a synthesized harmonic multiplier chain to drive a 5 W extended interaction klystron at 218.4 GHz, a mechanical mode mixer to illuminate and modulate many modes, and a heterodyne receiver coupled into a 60 cm scanning mirror. Large signal margins were obtained in this 50m range work, showing paths to imaging at 1km, imaging with considerably less powerful illuminators, and the use of focal plane arrays.

© 2012 Optical Society of America

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    [CrossRef]
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    [CrossRef]
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    [CrossRef]
  27. N. George, A. Jain, and R. D. S. Melville, “Experiments on the space and wavelength dependence of speckle,” Appl. Phys. 7, 157–169 (1975).
    [CrossRef]
  28. J. W. Goodman, “Dependence of image speckle contrast on surface roughness,” Opt. Commun. 14, 324–327 (1975).
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  29. J. W. Goodman, “Some fundamental properties of speckle,” J. Opt. Soc. Am. 66, 1145–1150 (1976).
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    [CrossRef]
  35. F. Qi, V. Tavakol, D. Schreurs, and B. Nauwelaers, “Limitations of approximations towards Fourier optics for indoor active millimeter wave imaging systems,” Prog. Electromagn. Res. 109, 245–262 (2010).
    [CrossRef]
  36. F. Qi, V. Tavakol, I. Ocket, P. Xu, D. Schreurs, J. Wang, and B. Nauwelaers, “Millimeter wave imaging system modeling: spatial frequency domain calculation versus spatial domain calculation,” J. Opt. Soc. Am. A 27, 131–140 (2010).
    [CrossRef]

2012 (1)

D. T. Petkie, J. Holt, M. A. Patrick, and F. C. De Lucia, “Multimode illumination in the terahertz for elimination of target orientation requirements and minimization of coherent effects in active imaging systems,” Opt. Eng. 51, 091604 (2012).
[CrossRef]

2011 (2)

W. Caba and G. D. Boreman, “Active sparse-aperture millimeter-wave imaging using digital correlators,” J. Infrared Millim. Terahertz Waves 32, 434–450 (2011).
[CrossRef]

S. Yeom, D.-S. Lee, J.-Y. Son, M.-K. Jung, Y. Jang, S.-W. Jung, and S.-J. Lee, “Real-time outdoor concealed-object detection with passive millimeter wave imaging,” Opt. Express 19, 2530–2536 (2011).
[CrossRef]

2010 (6)

F. Qi, V. Tavakol, I. Ocket, P. Xu, D. Schreurs, J. Wang, and B. Nauwelaers, “Millimeter wave imaging system modeling: spatial frequency domain calculation versus spatial domain calculation,” J. Opt. Soc. Am. A 27, 131–140 (2010).
[CrossRef]

H. B. Wallace, “Analysis of RF imaging applications at frequencies over 100 GHz,” Appl. Opt. 49, E38–E47 (2010).
[CrossRef]

E. Grossman, C. Dietlein, J. Ala-Laurinaho, M. Leivo, L. Gronberg, M. Gronholm, P. Lappalainen, A. Rautiainen, A. Tamminen, and A. Luukanen, “Passive terahertz camera for standoff security screening,” Appl. Opt. 49, E106–E120(2010).
[CrossRef]

K. B. Cooper, R. J. Denglera, N. Llombartb, A. Talukdera, A. V. Panangadana, C. S. Peaya, I. Mehdia, and P. H. Siegel, “Fast, high-resolution terahertz radar imaging at 25 meters,” Proc. SPIE 7671, 76710Y (2010).

Q. Li, S.-H. Ding, R. Yao, and Q. Wang, “Real-time terahertz scanning imaging by use of a pyroelectric array camera and image denoising,” J. Opt. Soc. Am. 27, 2381–2386 (2010).
[CrossRef]

F. Qi, V. Tavakol, D. Schreurs, and B. Nauwelaers, “Limitations of approximations towards Fourier optics for indoor active millimeter wave imaging systems,” Prog. Electromagn. Res. 109, 245–262 (2010).
[CrossRef]

2009 (1)

C. am Weg, W. von Spiegel, R. Henneberger, R. Zimmermann, T. Loeffler, and H. G. Roskos, “Fast active THz cameras with ranging capabilities,” J. Infrared Millim. Terahertz Waves 30, 1281–1296 (2009).

2008 (5)

2006 (1)

2004 (3)

F. C. De Lucia, “Noise, detectors, and submillimeter-terahertz system performance in nonambient environments,” J. Opt. Soc. Am. B 21, 1273–1297 (2004).
[CrossRef]

E. N. Grossman, A. Luukanen, and A. J. Miller, “Terahertz active direct detection imagers,” Proc. SPIE 5411, 68–77 (2004).
[CrossRef]

A. Luukanen, A. J. Miller, and E. N. Grossman, “Active millimeter-wave video rate imaging with a staring 120-element microbolometer array,” Proc. SPIE 5410, 195–210 (2004).
[CrossRef]

2003 (1)

P. Coward and R. Appleby, “Development of an illumination chamber for indoor millimetre-wave imaging,” Proc. SPIE 5077, 54–61 (2003).
[CrossRef]

2002 (1)

T. D. Dorney, W. W. Symes, R. G. Baraniuk, and D. M. Mittleman, “Terahertz multistatic reflection imaging,” J. Opt. Soc. Am. 19, 1432–1442 (2002).
[CrossRef]

2001 (1)

D. M. Sheen, D. L. McMakin, and T. E. Hall, “Three-dimensional millimeter-wave imaging for concealed weapon detection,” IEEE Trans. Microwave Theor. Tech. 49, 1581–1592 (2001).
[CrossRef]

1998 (1)

Y.-W. Chang and M. Johnson, “Portable concealed weapon detection using millimeter wave FMCW radar imaging,” Proc. SPIE 4232, 134–141 (1998).

1980 (1)

P. W. Kruse, “Why the military interest in near-millimeter wave imaging?” Proc. SPIE 259, 94–97 (1980).
[CrossRef]

1976 (2)

1975 (2)

N. George, A. Jain, and R. D. S. Melville, “Experiments on the space and wavelength dependence of speckle,” Appl. Phys. 7, 157–169 (1975).
[CrossRef]

J. W. Goodman, “Dependence of image speckle contrast on surface roughness,” Opt. Commun. 14, 324–327 (1975).
[CrossRef]

1973 (1)

1964 (1)

E. H. Putley, “The ultimate sensitivity of sub-mm detectors,” Infrared Phys. 4, 1–8 (1964).
[CrossRef]

1947 (1)

W. B. Lewis, “Fluctuations in streams of thermal radiation,” Proc. Phys. Soc 59, 34–40 (1947).
[CrossRef]

Ala-Laurinaho, J.

Alexander, N. E.

N. E. Alexander, C. C. Andres, and R. Gonzalo, “Multispectral mm-wave imaging: materials and images,” Proc. SPIE 6948, 694803 (2008).
[CrossRef]

am Weg, C.

C. am Weg, W. von Spiegel, R. Henneberger, R. Zimmermann, T. Loeffler, and H. G. Roskos, “Fast active THz cameras with ranging capabilities,” J. Infrared Millim. Terahertz Waves 30, 1281–1296 (2009).

Andres, C. C.

N. E. Alexander, C. C. Andres, and R. Gonzalo, “Multispectral mm-wave imaging: materials and images,” Proc. SPIE 6948, 694803 (2008).
[CrossRef]

Appleby, R.

P. Coward and R. Appleby, “Development of an illumination chamber for indoor millimetre-wave imaging,” Proc. SPIE 5077, 54–61 (2003).
[CrossRef]

Baraniuk, R. G.

T. D. Dorney, W. W. Symes, R. G. Baraniuk, and D. M. Mittleman, “Terahertz multistatic reflection imaging,” J. Opt. Soc. Am. 19, 1432–1442 (2002).
[CrossRef]

Bennett, J. S.

Bittner, D. N.

D. N. Bittner, R. L. Crownover, F. C. De Lucia, and S. L. Shostak, “Passive imaging with a broadband cooled detector,” in 12th International Conference on Infrared and Millimeter Waves (IEEE, 1987).

Boreman, G. D.

W. Caba and G. D. Boreman, “Active sparse-aperture millimeter-wave imaging using digital correlators,” J. Infrared Millim. Terahertz Waves 32, 434–450 (2011).
[CrossRef]

T. W. Du Bosq, J. M. Lopez-Alonso, and G. D. Boreman, “Millimeter wave imaging system for land mine detection,” Appl. Opt. 45, 5686–5692 (2006).
[CrossRef]

Brown, E. A.

S. M. Kulpa and E. A. Brown, Near-Millimeter Wave Technology Base Study (Harry Diamond Laboratories, 1979).

Caba, W.

W. Caba and G. D. Boreman, “Active sparse-aperture millimeter-wave imaging using digital correlators,” J. Infrared Millim. Terahertz Waves 32, 434–450 (2011).
[CrossRef]

Casto, C.

Chang, Y.-W.

Y.-W. Chang and M. Johnson, “Portable concealed weapon detection using millimeter wave FMCW radar imaging,” Proc. SPIE 4232, 134–141 (1998).

Christensen, C. R.

Cooper, K. B.

K. B. Cooper, R. J. Denglera, N. Llombartb, A. Talukdera, A. V. Panangadana, C. S. Peaya, I. Mehdia, and P. H. Siegel, “Fast, high-resolution terahertz radar imaging at 25 meters,” Proc. SPIE 7671, 76710Y (2010).

Coward, P.

P. Coward and R. Appleby, “Development of an illumination chamber for indoor millimetre-wave imaging,” Proc. SPIE 5077, 54–61 (2003).
[CrossRef]

Crownover, R. L.

D. N. Bittner, R. L. Crownover, F. C. De Lucia, and S. L. Shostak, “Passive imaging with a broadband cooled detector,” in 12th International Conference on Infrared and Millimeter Waves (IEEE, 1987).

De Lucia, F. C.

D. T. Petkie, J. Holt, M. A. Patrick, and F. C. De Lucia, “Multimode illumination in the terahertz for elimination of target orientation requirements and minimization of coherent effects in active imaging systems,” Opt. Eng. 51, 091604 (2012).
[CrossRef]

D. T. Petkie, C. Casto, F. C. De Lucia, S. R. Murrill, B. Redman, R. L. Espinola, C. C. Franck, E. L. Jacobs, S. T. Griffin, C. E. Halford, J. Reynolds, S. O’Brien, and D. Tofsted, “Active and passive imaging in the THz spectral region: phenomenology, dynamic range, modes, and illumination,” J. Opt. Soc. Am. B 25, 1523–1531 (2008).
[CrossRef]

F. C. De Lucia, “Noise, detectors, and submillimeter-terahertz system performance in nonambient environments,” J. Opt. Soc. Am. B 21, 1273–1297 (2004).
[CrossRef]

D. N. Bittner, R. L. Crownover, F. C. De Lucia, and S. L. Shostak, “Passive imaging with a broadband cooled detector,” in 12th International Conference on Infrared and Millimeter Waves (IEEE, 1987).

Denglera, R. J.

K. B. Cooper, R. J. Denglera, N. Llombartb, A. Talukdera, A. V. Panangadana, C. S. Peaya, I. Mehdia, and P. H. Siegel, “Fast, high-resolution terahertz radar imaging at 25 meters,” Proc. SPIE 7671, 76710Y (2010).

Dietlein, C.

Ding, S.-H.

Q. Li, S.-H. Ding, R. Yao, and Q. Wang, “Real-time terahertz scanning imaging by use of a pyroelectric array camera and image denoising,” J. Opt. Soc. Am. 27, 2381–2386 (2010).
[CrossRef]

Dorney, T. D.

T. D. Dorney, W. W. Symes, R. G. Baraniuk, and D. M. Mittleman, “Terahertz multistatic reflection imaging,” J. Opt. Soc. Am. 19, 1432–1442 (2002).
[CrossRef]

Du Bosq, T. W.

Elhawil, A.

Espinola, R. L.

Feng, Q.

Franck, C. C.

George, N.

Gonzalo, R.

N. E. Alexander, C. C. Andres, and R. Gonzalo, “Multispectral mm-wave imaging: materials and images,” Proc. SPIE 6948, 694803 (2008).
[CrossRef]

Goodman, J. W.

J. W. Goodman, “Some fundamental properties of speckle,” J. Opt. Soc. Am. 66, 1145–1150 (1976).
[CrossRef]

J. W. Goodman, “Dependence of image speckle contrast on surface roughness,” Opt. Commun. 14, 324–327 (1975).
[CrossRef]

J. W. Goodman, Speckle Phenomena in Optics: Theory and Applications (Roberts, 2007).

Griffin, S. T.

Gronberg, L.

Gronholm, M.

Grossman, E.

Grossman, E. N.

A. Luukanen, A. J. Miller, and E. N. Grossman, “Active millimeter-wave video rate imaging with a staring 120-element microbolometer array,” Proc. SPIE 5410, 195–210 (2004).
[CrossRef]

E. N. Grossman, A. Luukanen, and A. J. Miller, “Terahertz active direct detection imagers,” Proc. SPIE 5411, 68–77 (2004).
[CrossRef]

Guenther, B. D.

Halford, C. E.

Hall, T. E.

D. M. Sheen, D. L. McMakin, and T. E. Hall, “Three-dimensional millimeter-wave imaging for concealed weapon detection,” IEEE Trans. Microwave Theor. Tech. 49, 1581–1592 (2001).
[CrossRef]

Henneberger, R.

C. am Weg, W. von Spiegel, R. Henneberger, R. Zimmermann, T. Loeffler, and H. G. Roskos, “Fast active THz cameras with ranging capabilities,” J. Infrared Millim. Terahertz Waves 30, 1281–1296 (2009).

Holt, J.

D. T. Petkie, J. Holt, M. A. Patrick, and F. C. De Lucia, “Multimode illumination in the terahertz for elimination of target orientation requirements and minimization of coherent effects in active imaging systems,” Opt. Eng. 51, 091604 (2012).
[CrossRef]

Islam, S.

Jacobs, E. L.

Jaeger, I.

Jäger, I.

Jain, A.

N. George, A. Jain, and R. D. S. Melville, “Experiments on the space and wavelength dependence of speckle,” Appl. Phys. 7, 157–169 (1975).
[CrossRef]

N. George and A. Jain, “Speckle reduction using multiple tones of illumination,” Appl. Opt. 12, 1202–1212 (1973).
[CrossRef]

Jang, Y.

Johnson, M.

Y.-W. Chang and M. Johnson, “Portable concealed weapon detection using millimeter wave FMCW radar imaging,” Proc. SPIE 4232, 134–141 (1998).

Jung, M.-K.

Jung, S.-W.

Koers, G.

Kruse, P. W.

P. W. Kruse, “Why the military interest in near-millimeter wave imaging?” Proc. SPIE 259, 94–97 (1980).
[CrossRef]

Kulpa, S. M.

S. M. Kulpa and E. A. Brown, Near-Millimeter Wave Technology Base Study (Harry Diamond Laboratories, 1979).

Lappalainen, P.

Lee, D.-S.

Lee, S.-J.

Leivo, M.

Lewis, W. B.

W. B. Lewis, “Fluctuations in streams of thermal radiation,” Proc. Phys. Soc 59, 34–40 (1947).
[CrossRef]

Li, Q.

Q. Li, S.-H. Ding, R. Yao, and Q. Wang, “Real-time terahertz scanning imaging by use of a pyroelectric array camera and image denoising,” J. Opt. Soc. Am. 27, 2381–2386 (2010).
[CrossRef]

Llombartb, N.

K. B. Cooper, R. J. Denglera, N. Llombartb, A. Talukdera, A. V. Panangadana, C. S. Peaya, I. Mehdia, and P. H. Siegel, “Fast, high-resolution terahertz radar imaging at 25 meters,” Proc. SPIE 7671, 76710Y (2010).

Loeffler, T.

C. am Weg, W. von Spiegel, R. Henneberger, R. Zimmermann, T. Loeffler, and H. G. Roskos, “Fast active THz cameras with ranging capabilities,” J. Infrared Millim. Terahertz Waves 30, 1281–1296 (2009).

Lopez-Alonso, J. M.

Luukanen, A.

E. Grossman, C. Dietlein, J. Ala-Laurinaho, M. Leivo, L. Gronberg, M. Gronholm, P. Lappalainen, A. Rautiainen, A. Tamminen, and A. Luukanen, “Passive terahertz camera for standoff security screening,” Appl. Opt. 49, E106–E120(2010).
[CrossRef]

A. Luukanen, A. J. Miller, and E. N. Grossman, “Active millimeter-wave video rate imaging with a staring 120-element microbolometer array,” Proc. SPIE 5410, 195–210 (2004).
[CrossRef]

E. N. Grossman, A. Luukanen, and A. J. Miller, “Terahertz active direct detection imagers,” Proc. SPIE 5411, 68–77 (2004).
[CrossRef]

McMakin, D. L.

D. M. Sheen, D. L. McMakin, and T. E. Hall, “Three-dimensional millimeter-wave imaging for concealed weapon detection,” IEEE Trans. Microwave Theor. Tech. 49, 1581–1592 (2001).
[CrossRef]

Mehdia, I.

K. B. Cooper, R. J. Denglera, N. Llombartb, A. Talukdera, A. V. Panangadana, C. S. Peaya, I. Mehdia, and P. H. Siegel, “Fast, high-resolution terahertz radar imaging at 25 meters,” Proc. SPIE 7671, 76710Y (2010).

Melville, R. D. S.

N. George, A. Jain, and R. D. S. Melville, “Experiments on the space and wavelength dependence of speckle,” Appl. Phys. 7, 157–169 (1975).
[CrossRef]

Miller, A. J.

E. N. Grossman, A. Luukanen, and A. J. Miller, “Terahertz active direct detection imagers,” Proc. SPIE 5411, 68–77 (2004).
[CrossRef]

A. Luukanen, A. J. Miller, and E. N. Grossman, “Active millimeter-wave video rate imaging with a staring 120-element microbolometer array,” Proc. SPIE 5410, 195–210 (2004).
[CrossRef]

Mittleman, D. M.

T. D. Dorney, W. W. Symes, R. G. Baraniuk, and D. M. Mittleman, “Terahertz multistatic reflection imaging,” J. Opt. Soc. Am. 19, 1432–1442 (2002).
[CrossRef]

Murrill, S. R.

Nauwelaers, B.

F. Qi, V. Tavakol, D. Schreurs, and B. Nauwelaers, “Limitations of approximations towards Fourier optics for indoor active millimeter wave imaging systems,” Prog. Electromagn. Res. 109, 245–262 (2010).
[CrossRef]

F. Qi, V. Tavakol, I. Ocket, P. Xu, D. Schreurs, J. Wang, and B. Nauwelaers, “Millimeter wave imaging system modeling: spatial frequency domain calculation versus spatial domain calculation,” J. Opt. Soc. Am. A 27, 131–140 (2010).
[CrossRef]

G. Koers, I. Ocket, Q. Feng, V. Tavakol, I. Jäger, B. Nauwelaers, and J. Stiens, “Study of active millimeter-wave image speckle reduction by Hadamard phase pattern illumination,” J. Opt. Soc. Am. A 25, 312–317 (2008).
[CrossRef]

I. Ocket, D. Schreurs, V. Tavakol, F. Qi, B. Nauwelaers, and J. Stiens, “Design challenges for millimeter wave active imaging systems,” in Proceedings of the 7th European Radar Conference (IEEE, 2010), pp. 312–315.

O’Brien, S.

Ocket, I.

Panangadana, A. V.

K. B. Cooper, R. J. Denglera, N. Llombartb, A. Talukdera, A. V. Panangadana, C. S. Peaya, I. Mehdia, and P. H. Siegel, “Fast, high-resolution terahertz radar imaging at 25 meters,” Proc. SPIE 7671, 76710Y (2010).

Patrick, M. A.

D. T. Petkie, J. Holt, M. A. Patrick, and F. C. De Lucia, “Multimode illumination in the terahertz for elimination of target orientation requirements and minimization of coherent effects in active imaging systems,” Opt. Eng. 51, 091604 (2012).
[CrossRef]

Peaya, C. S.

K. B. Cooper, R. J. Denglera, N. Llombartb, A. Talukdera, A. V. Panangadana, C. S. Peaya, I. Mehdia, and P. H. Siegel, “Fast, high-resolution terahertz radar imaging at 25 meters,” Proc. SPIE 7671, 76710Y (2010).

Petkie, D. T.

D. T. Petkie, J. Holt, M. A. Patrick, and F. C. De Lucia, “Multimode illumination in the terahertz for elimination of target orientation requirements and minimization of coherent effects in active imaging systems,” Opt. Eng. 51, 091604 (2012).
[CrossRef]

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[CrossRef]

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F. Qi, V. Tavakol, I. Ocket, P. Xu, D. Schreurs, J. Wang, and B. Nauwelaers, “Millimeter wave imaging system modeling: spatial frequency domain calculation versus spatial domain calculation,” J. Opt. Soc. Am. A 27, 131–140 (2010).
[CrossRef]

F. Qi, V. Tavakol, D. Schreurs, and B. Nauwelaers, “Limitations of approximations towards Fourier optics for indoor active millimeter wave imaging systems,” Prog. Electromagn. Res. 109, 245–262 (2010).
[CrossRef]

I. Ocket, D. Schreurs, V. Tavakol, F. Qi, B. Nauwelaers, and J. Stiens, “Design challenges for millimeter wave active imaging systems,” in Proceedings of the 7th European Radar Conference (IEEE, 2010), pp. 312–315.

Rautiainen, A.

Redman, B.

Reynolds, J.

Roskos, H. G.

C. am Weg, W. von Spiegel, R. Henneberger, R. Zimmermann, T. Loeffler, and H. G. Roskos, “Fast active THz cameras with ranging capabilities,” J. Infrared Millim. Terahertz Waves 30, 1281–1296 (2009).

Schreurs, D.

F. Qi, V. Tavakol, D. Schreurs, and B. Nauwelaers, “Limitations of approximations towards Fourier optics for indoor active millimeter wave imaging systems,” Prog. Electromagn. Res. 109, 245–262 (2010).
[CrossRef]

F. Qi, V. Tavakol, I. Ocket, P. Xu, D. Schreurs, J. Wang, and B. Nauwelaers, “Millimeter wave imaging system modeling: spatial frequency domain calculation versus spatial domain calculation,” J. Opt. Soc. Am. A 27, 131–140 (2010).
[CrossRef]

I. Ocket, D. Schreurs, V. Tavakol, F. Qi, B. Nauwelaers, and J. Stiens, “Design challenges for millimeter wave active imaging systems,” in Proceedings of the 7th European Radar Conference (IEEE, 2010), pp. 312–315.

Sheen, D. M.

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K. B. Cooper, R. J. Denglera, N. Llombartb, A. Talukdera, A. V. Panangadana, C. S. Peaya, I. Mehdia, and P. H. Siegel, “Fast, high-resolution terahertz radar imaging at 25 meters,” Proc. SPIE 7671, 76710Y (2010).

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Stiens, J.

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[CrossRef]

Talukdera, A.

K. B. Cooper, R. J. Denglera, N. Llombartb, A. Talukdera, A. V. Panangadana, C. S. Peaya, I. Mehdia, and P. H. Siegel, “Fast, high-resolution terahertz radar imaging at 25 meters,” Proc. SPIE 7671, 76710Y (2010).

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Tavakol, V.

F. Qi, V. Tavakol, D. Schreurs, and B. Nauwelaers, “Limitations of approximations towards Fourier optics for indoor active millimeter wave imaging systems,” Prog. Electromagn. Res. 109, 245–262 (2010).
[CrossRef]

F. Qi, V. Tavakol, I. Ocket, P. Xu, D. Schreurs, J. Wang, and B. Nauwelaers, “Millimeter wave imaging system modeling: spatial frequency domain calculation versus spatial domain calculation,” J. Opt. Soc. Am. A 27, 131–140 (2010).
[CrossRef]

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I. Ocket, D. Schreurs, V. Tavakol, F. Qi, B. Nauwelaers, and J. Stiens, “Design challenges for millimeter wave active imaging systems,” in Proceedings of the 7th European Radar Conference (IEEE, 2010), pp. 312–315.

Tofsted, D.

von Spiegel, W.

C. am Weg, W. von Spiegel, R. Henneberger, R. Zimmermann, T. Loeffler, and H. G. Roskos, “Fast active THz cameras with ranging capabilities,” J. Infrared Millim. Terahertz Waves 30, 1281–1296 (2009).

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Appl. Opt. (5)

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[CrossRef]

IEEE Trans. Microwave Theor. Tech. (1)

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[CrossRef]

Infrared Phys. (1)

E. H. Putley, “The ultimate sensitivity of sub-mm detectors,” Infrared Phys. 4, 1–8 (1964).
[CrossRef]

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[CrossRef]

C. am Weg, W. von Spiegel, R. Henneberger, R. Zimmermann, T. Loeffler, and H. G. Roskos, “Fast active THz cameras with ranging capabilities,” J. Infrared Millim. Terahertz Waves 30, 1281–1296 (2009).

J. Opt. Soc. Am. (4)

T. D. Dorney, W. W. Symes, R. G. Baraniuk, and D. M. Mittleman, “Terahertz multistatic reflection imaging,” J. Opt. Soc. Am. 19, 1432–1442 (2002).
[CrossRef]

Q. Li, S.-H. Ding, R. Yao, and Q. Wang, “Real-time terahertz scanning imaging by use of a pyroelectric array camera and image denoising,” J. Opt. Soc. Am. 27, 2381–2386 (2010).
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Opt. Eng. (1)

D. T. Petkie, J. Holt, M. A. Patrick, and F. C. De Lucia, “Multimode illumination in the terahertz for elimination of target orientation requirements and minimization of coherent effects in active imaging systems,” Opt. Eng. 51, 091604 (2012).
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[CrossRef]

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F. Qi, V. Tavakol, D. Schreurs, and B. Nauwelaers, “Limitations of approximations towards Fourier optics for indoor active millimeter wave imaging systems,” Prog. Electromagn. Res. 109, 245–262 (2010).
[CrossRef]

Other (5)

D. N. Bittner, R. L. Crownover, F. C. De Lucia, and S. L. Shostak, “Passive imaging with a broadband cooled detector,” in 12th International Conference on Infrared and Millimeter Waves (IEEE, 1987).

I. Ocket, D. Schreurs, V. Tavakol, F. Qi, B. Nauwelaers, and J. Stiens, “Design challenges for millimeter wave active imaging systems,” in Proceedings of the 7th European Radar Conference (IEEE, 2010), pp. 312–315.

S. M. Kulpa and E. A. Brown, Near-Millimeter Wave Technology Base Study (Harry Diamond Laboratories, 1979).

J. W. Goodman, Speckle Phenomena in Optics: Theory and Applications (Roberts, 2007).

A. Yariv, Quantum Electronics, 2nd ed. (Wiley, 1975).

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Figures (15)

Fig. 1.
Fig. 1.

(a) Indoor image of a face made with a passive bolometer system centered on 650GHz and (b) an image of a face made with an active illuminator and heterodyne receiver at 632 GHz.

Fig. 2.
Fig. 2.

Mirror covered with Eccosorb on left and right, with a thin scarf on top. In (a) the mirror is normal to the optical axis and in (b) the mirror is rotated by 20°.

Fig. 3.
Fig. 3.

(a) Image of an optimally oriented toy gun placed atop an optical breadboard with hole spacing of 2.54 cm and (b) an image of the same gun located in a reflective enclosure to provide illumination in many modes from many angles.

Fig. 4.
Fig. 4.

(a) Image of a knife under a thin brown robe at 632 GHz. (c) Co-added image of a knife taken at 16 independent angles as defined by Eq. (15). The quantitative traces below each image show the signal along the blue line in each image. These graphs show that the speckle contrast noise is reduced by (16)1/2=4 by the averaging over the 16 independent images. A more formal analysis of the speckle in the red (left) and green (right) boxes is presented in Subsection 6.B.

Fig. 5.
Fig. 5.

Mode mixing illumination and scanning receiver system. The power for the transmitter of this system originates is a 5 W EIK whose output illuminates a rotating rooftop mirror and reflects off of a second mirror that can be adjusted in angle, so as to illuminate many modes sequentially. The heterodyne receiver sits at the focus of a 60 cm diameter, 1 m focal length mirror, which is scanned to form the image.

Fig. 6.
Fig. 6.

Optical image of the atrium of the Physics Building at Ohio State University.

Fig. 7.
Fig. 7.

(a) 218.4 GHz image of the atrium of the Physics Building at Ohio State University with multimode illumination, but without modulated mode mixing and (b) with modulated mode mixing. The colored boxes show areas for which speckle statistics have been calculated.

Fig. 8.
Fig. 8.

Experimental intensities of image points (red crosses) and curve fitted to Eq. (23) (blue line) for image points inside the red (left) box of the upper image of Fig. 4 and green (right) box, corresponding to (a) and (b) here.

Fig. 9.
Fig. 9.

Experimental intensities of image points (red crosses) and curve fitted to Eq. (23) (blue line) for image points inside the red (left) box and green (right) box of the lower image of Fig. 4, corresponding to (a) and (b) here.

Fig. 10.
Fig. 10.

Fits to the Gamma function of Eq. (23) for the image within the orange (left), green (squares), and blue (right) boxes in Fig. 7, corresponding to (a), (b), and (c) here.

Fig. 11.
Fig. 11.

Fits to the Rician function of Eq. (24) for the image within the orange (left), green (squares), and blue (right) boxes of the upper panel in Fig. 7, corresponding to (a), (b), and (c) here.

Fig. 12.
Fig. 12.

Fits to the Gamma function of Eq. (23) for the averaged image within the orange left), green (squares), and blue (right) boxes in the lower panel of Fig. 7, corresponding to (a), (b), and (c) here.

Fig. 13.
Fig. 13.

Fits to the Rician function of Eq. (24) for the mode mixed image within the orange (left), green (squares), and blue (right) boxes in the lower panel of Fig. 7, corresponding to (a), (b), and (c) here.

Fig. 14.
Fig. 14.

Intensity distributions for the image without mode modulation. The red (lower) curve is the intensity distribution from the red box with specular and diffuse reflections. The green (upper) curve is from the green box with mostly diffuse reflections.

Fig. 15.
Fig. 15.

Conceptual urban canyon application (courtesy M. Rosker).

Tables (1)

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Table 1. Comparison of Illumination Temperatures

Equations (27)

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Pn=NEP·B1/2.
PnkT(Bνmax)1/2=kTνmax(Bνmax)1/2
NEP=kTνmax1/2.
Pn=kTn(Bb)1/2,
ΔT=Tn(Bb)1/2.
Pn=kTn(Bb)1/2=NEP(Bb)1/2.
NEPb1/2=NEPequiv
NEPequiv=4·1015W/Hz1/2.
Tn=NEPk=NEPequivkb1/2109K.
C=σI
δνν=λσh1C418π2,
AS=(λrtoDo)2.
N=2πASλ2=2π(rtoDo)2
2ΘspDor
θDorto,
C=1/16=0.25.
Teff=Pkb,
Ω=λ2A.
A2π=λ22π.
N2π=2π2A2π=4π22λ2
Psm=PRA2π2πl2=PR14π2λ2l2=kTeffb,
N2π=4π2l2λ2=4π2·1010.
pI(I)=NNIN1Γ(N)INeNII,
pI(I)=1Ine(IIn+r)I0(2IInr),
C=1+2r1+r.
N=2πr2D02=2π·104.
N=(DsD0)2=400.

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