Abstract

Natural cork enclosures, due to their cell structure, composition, and low moisture are fairly transparent to terahertz (THz) and millimeter waves enabling nondestructive evaluation of the cork's surface and interior. It is shown that the attenuation coefficient of the defect-free cork can be modeled with a Mie scattering model in the weakly scattering limit. Contrast in the THz images is a result of enhanced scattering of THz radiation by defects or voids as well as variations in the cork cell structure. The presence of voids, defects, and changes in grain structure can be determined with roughly 100300  μm resolution.

© 2008 Optical Society of America

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References

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  1. J. Chang, G. Han, J. M. Valverde, N. C. Griswold, J. F. Duque-Carrillo, and E. Sanchez-Sinencio, "Cork quality classification system using a unified image processing and fuzzy-neural network methodology," IEEE Trans. Neural Netw. 8, 964-974 (1997).
    [CrossRef] [PubMed]
  2. R. Juanola, D. Subirà, V. Salvadó, J. A. Garcia Regueiro, and E. Anticó, "Evaluation of an extraction method in the determination of the 2,4,6-trichloroanisole content of tainted cork," J. Chromatogr. A 953, 207-214 (2002).
    [CrossRef] [PubMed]
  3. E. Lizarraga, Á. Irigoyen, V. Belsue, and E. González-Peñas, "Determination of chloroanisole compounds in red wine by headspace solid-phase microextraction and gas chromatography-mass spectrometry," J. Chromatogr. A 1052, 145-149 (2004).
    [CrossRef] [PubMed]
  4. E. Herve, S. Price, G. Burns, and P. Weber, presented at the ASEV Annual Meeting, Reno, Nevada, 2 July 1999. http://www.corkqc.com/asev/asev2-2.htm.
  5. A. Brunetti, R. Cesareo, B. Golosio, P. Luciano, and A. Ruggero, "Cork quality estimation by using Compton tomography," Nucl. Instrum. Methods Phys. Res. B 196, 161-168 (2002).
    [CrossRef]
  6. D. Zimdars, J. S. White, G. Stuk, A. Chernovsky, G. Fichter, and S. Williamson, "Large area terahertz imaging and non-destructive evaluation applications," Insight-Non-Destruct. Test. Condition Monitor. 48, 537-539 (2006).
    [CrossRef]
  7. D. Zimdars, J. A. Valdmanis, J. S. White, G. Stuk, W. P. Winfree, and E. I. Madaras, "Time domain terahertz detection of flaws within space shuttle sprayed on foam insulation," in Conference on Lasers and Electro-Optics/(CLEO), Vol. 96 of OSA Trends in Optics and Photonics (Optical Society of America, 2004), paper CThN4. http://www.opticsinfobase.org/abstract.cfm?id=104293.
  8. H. S. Chua, P. C. Upadhya, A. D. Haigh, J. Obradovic, A. A. P. Gibson, and E. H. Linfield, "Terahertz time-domain spectroscopy of wheat grain," in Conference Digest of the 2004 Joint 29th International Conference on Infrared and Millimeter Waves and 12th International Conference on Terahertz Electronics (IEEE, 2004), pp. 399-400.
    [CrossRef]
  9. H. S. Chua, J. Obradovic, A. D. Haigh, P. C. Upadhya, O. Hirsch, D. Crawley, A. A. P. Gibson, and E. H. Linfield, "Terahertz time-domain spectroscopy of crushed wheat grain," in 2005 IEEE MTT-S International Microwave Symposium (IEEE, 2005), p. 4.
  10. S. Hadjiloucas, L. S. Karatzas, and J. W. Bowen, "Measurements of leaf water content using terahertz radiation," IEEE Trans. Microwave Theory Tech. 47, 142-149 (1999).
    [CrossRef]
  11. S. Hadjiloucas, R. K. H. Galvao, and J. W. J. Bowen, "Analysis of spectroscopic measurements of leaf water content at terahertz frequencies using linear transforms," J. Opt. Soc. Am. A 19, 2495-2509 (2002).
    [CrossRef]
  12. M. Reid and R. Fedosejevs, "Terahertz birefringence and attenuation properties of wood and paper," Appl. Opt. 45, 2766-2772 (2006).
    [CrossRef] [PubMed]
  13. C. J. Strachan, T. Rades, D. A. Newnham, K. C. Gordon, M. Pepper, and P. F. Taday, "Using terahertz pulsed spectroscopy to study crystallinity of pharmaceutical materials," Chem. Phys. Lett. 390, 20-24 (2004).
    [CrossRef]
  14. D. S. Venables and C. A. Schmuttenmaer, "Spectroscopy and dynamics of mixtures of water with acetone, acetonitrile, and methanol," J. Chem. Phys. 113, 11222-11236 (2000).
    [CrossRef]
  15. J. F. Federici, B. Schulkin, F. Huang, D. Gary, R. Barat, F. Oliveira, and D. Zimdars, "THz imaging and sensing for security applications-explosives, weapons and drugs," Semicond. Sci. Technol. 20, S266-S280 (2005).
    [CrossRef]
  16. J. F. Federici, D. Gary, R. Barat, and Z.-H. Michalopoulou, "Detection of Explosives by Terahertz Imaging," in Counter-Terrorism Detection Techniques of Explosives, J. Yinon, ed. (Elsevier, 2007).
    [CrossRef]
  17. F. C. Delucia, "Spectroscopy in the terahertz spectral region," in Sensing with Terahertz Radiation, D. Mittleman ed. (Springer, 2003).
  18. M. C. Beard, G. M. Turner, and C. A. Schmuttenmaer, "THz spectroscopy," J. Phys. Chem B 106, 7146-7159 (2002).
    [CrossRef]
  19. Y. L. Hor, H. C. Lim, J. F. Federici, E. Moore, and J. W. Bozzelli, "Terahertz spectroscopy of trichloroanisole," (submitted to Chem. Phys. Lett.).
  20. F. Huang, B. Schulkin, H. Altan, J. Federici, D. Gary, R. Barat, D. Zimdars, M. Chen, and D. 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]
  21. A. Nystrom, A. Grimvall, C. Krantz-Rulcker, R. Savenhed, and K. Akerstrand, "Water off-flavour caused by 2,4,6-trichloroanisole," Water Sci. Technol. 25, 241-249 (1992).
  22. S. Karlsson, S. Kaugare, A. Grimvall, H. Boren, and R. Savenhed, "Formation of 2,4,6-trichlorophenol and 2,4,6-trichloroanisole during treatment and distribution of drinking water," Water Sci. Technol. 31, 99-103 (1995).
    [CrossRef]
  23. A. Miki, A. Isogai, H. Utsunomiya, and H. Iwata, "Identification of 2,4,6-trichloroanisole (TCA) causing a musty/muddy off-flavor in sake and its production in rice koji and moromi mash," J. Biosci. Bioeng. 100, 178-183 (2005).
    [CrossRef] [PubMed]
  24. L. H. Aung, J. L. Smilanick, P. V. Vail, P. L. Hartsell, and E. Gomez, "Investigations into the origin of chloroanisoles causing musty off-flavor of raisins," J. Agric. Food Chem. 44, 3294-3296 (1996).
    [CrossRef]
  25. C. Silva Pereira, J. J. Figueiredo Marques, and M. V. San Romao, "Cork taint in wine: scientific knowledge and public perception--a critical review," Crit. Rev. Microbiol. 26, 147-162 (2000).
    [CrossRef] [PubMed]
  26. A. P. Pollnitz, K. H. Pardon, D. Liacopoulos, G. K. Skouroumounis, and M. A. Sefton, "The analysis of 2,4,6-trichloroanisole and other chloroanisoles in tainted wines and corks," Aust. J. Grape Win. Res. 2, 184-190 (1996).
    [CrossRef]
  27. J. Gunschera, F. Fuhrmann, T. Salthammer, A. Schulze, and E. Uhde, "Formation and emission of chloroanisoles as indoor pollutants," Environ. Sci. Pollut. Res. 11, 147-151 (2004).
    [CrossRef]
  28. J. Prescott, L. Norris, M. Kunst, and S. Kim, "Estimating a consumer rejection threshold for cork taint in white wine," Food Qual. Pref. 16, 345-349 (2005).
    [CrossRef]
  29. D. Mittleman, "Terahertz imaging," in Sensing with Terahertz Radiation, D. Mittleman, ed. (Springer, 2003).
  30. A. Sengupta, A. Bandyopadhyay, J. F. Federici, R. B. Barat, D. E. Gary, M. Chen, and D. B. Tanner, "Effects of scattering on THz spectra of granular solids," Int. J. Infrared Millim. Waves (to be published).
  31. D. M. Mittleman, S. Hunsche, L. Boivin, and M. C. Nuss, "T-ray tomography," Opt. Lett. 22, 904-906 (1997).
    [CrossRef] [PubMed]
  32. T. Yasui, T. Yasuda, T. Araki, and E. Abraham, "Real-time two-dimensional terahertz tomography of moving objects," Opt. Commun. 267, 128-136 (2006).
    [CrossRef]
  33. H. Zhong, J. Xu, X. Xie, T. Yuan, R. Reightler, E. Madaras, and X.-C. Zhang, "Nondestructive defect identification with terahertz time-of-flight tomography," IEEE Sens. J. 5, 203-208 (2005).
    [CrossRef]

2006 (3)

D. Zimdars, J. S. White, G. Stuk, A. Chernovsky, G. Fichter, and S. Williamson, "Large area terahertz imaging and non-destructive evaluation applications," Insight-Non-Destruct. Test. Condition Monitor. 48, 537-539 (2006).
[CrossRef]

T. Yasui, T. Yasuda, T. Araki, and E. Abraham, "Real-time two-dimensional terahertz tomography of moving objects," Opt. Commun. 267, 128-136 (2006).
[CrossRef]

M. Reid and R. Fedosejevs, "Terahertz birefringence and attenuation properties of wood and paper," Appl. Opt. 45, 2766-2772 (2006).
[CrossRef] [PubMed]

2005 (4)

J. Prescott, L. Norris, M. Kunst, and S. Kim, "Estimating a consumer rejection threshold for cork taint in white wine," Food Qual. Pref. 16, 345-349 (2005).
[CrossRef]

H. Zhong, J. Xu, X. Xie, T. Yuan, R. Reightler, E. Madaras, and X.-C. Zhang, "Nondestructive defect identification with terahertz time-of-flight tomography," IEEE Sens. J. 5, 203-208 (2005).
[CrossRef]

J. F. Federici, B. Schulkin, F. Huang, D. Gary, R. Barat, F. Oliveira, and D. Zimdars, "THz imaging and sensing for security applications-explosives, weapons and drugs," Semicond. Sci. Technol. 20, S266-S280 (2005).
[CrossRef]

A. Miki, A. Isogai, H. Utsunomiya, and H. Iwata, "Identification of 2,4,6-trichloroanisole (TCA) causing a musty/muddy off-flavor in sake and its production in rice koji and moromi mash," J. Biosci. Bioeng. 100, 178-183 (2005).
[CrossRef] [PubMed]

2004 (4)

F. Huang, B. Schulkin, H. Altan, J. Federici, D. Gary, R. Barat, D. Zimdars, M. Chen, and D. 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]

C. J. Strachan, T. Rades, D. A. Newnham, K. C. Gordon, M. Pepper, and P. F. Taday, "Using terahertz pulsed spectroscopy to study crystallinity of pharmaceutical materials," Chem. Phys. Lett. 390, 20-24 (2004).
[CrossRef]

E. Lizarraga, Á. Irigoyen, V. Belsue, and E. González-Peñas, "Determination of chloroanisole compounds in red wine by headspace solid-phase microextraction and gas chromatography-mass spectrometry," J. Chromatogr. A 1052, 145-149 (2004).
[CrossRef] [PubMed]

J. Gunschera, F. Fuhrmann, T. Salthammer, A. Schulze, and E. Uhde, "Formation and emission of chloroanisoles as indoor pollutants," Environ. Sci. Pollut. Res. 11, 147-151 (2004).
[CrossRef]

2002 (4)

S. Hadjiloucas, R. K. H. Galvao, and J. W. J. Bowen, "Analysis of spectroscopic measurements of leaf water content at terahertz frequencies using linear transforms," J. Opt. Soc. Am. A 19, 2495-2509 (2002).
[CrossRef]

A. Brunetti, R. Cesareo, B. Golosio, P. Luciano, and A. Ruggero, "Cork quality estimation by using Compton tomography," Nucl. Instrum. Methods Phys. Res. B 196, 161-168 (2002).
[CrossRef]

R. Juanola, D. Subirà, V. Salvadó, J. A. Garcia Regueiro, and E. Anticó, "Evaluation of an extraction method in the determination of the 2,4,6-trichloroanisole content of tainted cork," J. Chromatogr. A 953, 207-214 (2002).
[CrossRef] [PubMed]

M. C. Beard, G. M. Turner, and C. A. Schmuttenmaer, "THz spectroscopy," J. Phys. Chem B 106, 7146-7159 (2002).
[CrossRef]

2000 (2)

C. Silva Pereira, J. J. Figueiredo Marques, and M. V. San Romao, "Cork taint in wine: scientific knowledge and public perception--a critical review," Crit. Rev. Microbiol. 26, 147-162 (2000).
[CrossRef] [PubMed]

D. S. Venables and C. A. Schmuttenmaer, "Spectroscopy and dynamics of mixtures of water with acetone, acetonitrile, and methanol," J. Chem. Phys. 113, 11222-11236 (2000).
[CrossRef]

1999 (1)

S. Hadjiloucas, L. S. Karatzas, and J. W. Bowen, "Measurements of leaf water content using terahertz radiation," IEEE Trans. Microwave Theory Tech. 47, 142-149 (1999).
[CrossRef]

1997 (2)

J. Chang, G. Han, J. M. Valverde, N. C. Griswold, J. F. Duque-Carrillo, and E. Sanchez-Sinencio, "Cork quality classification system using a unified image processing and fuzzy-neural network methodology," IEEE Trans. Neural Netw. 8, 964-974 (1997).
[CrossRef] [PubMed]

D. M. Mittleman, S. Hunsche, L. Boivin, and M. C. Nuss, "T-ray tomography," Opt. Lett. 22, 904-906 (1997).
[CrossRef] [PubMed]

1996 (2)

A. P. Pollnitz, K. H. Pardon, D. Liacopoulos, G. K. Skouroumounis, and M. A. Sefton, "The analysis of 2,4,6-trichloroanisole and other chloroanisoles in tainted wines and corks," Aust. J. Grape Win. Res. 2, 184-190 (1996).
[CrossRef]

L. H. Aung, J. L. Smilanick, P. V. Vail, P. L. Hartsell, and E. Gomez, "Investigations into the origin of chloroanisoles causing musty off-flavor of raisins," J. Agric. Food Chem. 44, 3294-3296 (1996).
[CrossRef]

1995 (1)

S. Karlsson, S. Kaugare, A. Grimvall, H. Boren, and R. Savenhed, "Formation of 2,4,6-trichlorophenol and 2,4,6-trichloroanisole during treatment and distribution of drinking water," Water Sci. Technol. 31, 99-103 (1995).
[CrossRef]

1992 (1)

A. Nystrom, A. Grimvall, C. Krantz-Rulcker, R. Savenhed, and K. Akerstrand, "Water off-flavour caused by 2,4,6-trichloroanisole," Water Sci. Technol. 25, 241-249 (1992).

Appl. Opt. (1)

Appl. Phys. Lett (1)

F. Huang, B. Schulkin, H. Altan, J. Federici, D. Gary, R. Barat, D. Zimdars, M. Chen, and D. 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]

Aust. J. Grape Win. Res. (1)

A. P. Pollnitz, K. H. Pardon, D. Liacopoulos, G. K. Skouroumounis, and M. A. Sefton, "The analysis of 2,4,6-trichloroanisole and other chloroanisoles in tainted wines and corks," Aust. J. Grape Win. Res. 2, 184-190 (1996).
[CrossRef]

Chem. Phys. Lett. (1)

C. J. Strachan, T. Rades, D. A. Newnham, K. C. Gordon, M. Pepper, and P. F. Taday, "Using terahertz pulsed spectroscopy to study crystallinity of pharmaceutical materials," Chem. Phys. Lett. 390, 20-24 (2004).
[CrossRef]

Crit. Rev. Microbiol. (1)

C. Silva Pereira, J. J. Figueiredo Marques, and M. V. San Romao, "Cork taint in wine: scientific knowledge and public perception--a critical review," Crit. Rev. Microbiol. 26, 147-162 (2000).
[CrossRef] [PubMed]

Environ. Sci. Pollut. Res. (1)

J. Gunschera, F. Fuhrmann, T. Salthammer, A. Schulze, and E. Uhde, "Formation and emission of chloroanisoles as indoor pollutants," Environ. Sci. Pollut. Res. 11, 147-151 (2004).
[CrossRef]

Food Qual. Pref. (1)

J. Prescott, L. Norris, M. Kunst, and S. Kim, "Estimating a consumer rejection threshold for cork taint in white wine," Food Qual. Pref. 16, 345-349 (2005).
[CrossRef]

IEEE Sens. J. (1)

H. Zhong, J. Xu, X. Xie, T. Yuan, R. Reightler, E. Madaras, and X.-C. Zhang, "Nondestructive defect identification with terahertz time-of-flight tomography," IEEE Sens. J. 5, 203-208 (2005).
[CrossRef]

IEEE Trans. Microwave Theory Tech. (1)

S. Hadjiloucas, L. S. Karatzas, and J. W. Bowen, "Measurements of leaf water content using terahertz radiation," IEEE Trans. Microwave Theory Tech. 47, 142-149 (1999).
[CrossRef]

IEEE Trans. Neural Netw. (1)

J. Chang, G. Han, J. M. Valverde, N. C. Griswold, J. F. Duque-Carrillo, and E. Sanchez-Sinencio, "Cork quality classification system using a unified image processing and fuzzy-neural network methodology," IEEE Trans. Neural Netw. 8, 964-974 (1997).
[CrossRef] [PubMed]

Insight-Non-Destruct. Test. Condition Monitor. (1)

D. Zimdars, J. S. White, G. Stuk, A. Chernovsky, G. Fichter, and S. Williamson, "Large area terahertz imaging and non-destructive evaluation applications," Insight-Non-Destruct. Test. Condition Monitor. 48, 537-539 (2006).
[CrossRef]

Int. J. Infrared Millim. Waves (1)

A. Sengupta, A. Bandyopadhyay, J. F. Federici, R. B. Barat, D. E. Gary, M. Chen, and D. B. Tanner, "Effects of scattering on THz spectra of granular solids," Int. J. Infrared Millim. Waves (to be published).

J. Agric. Food Chem. (1)

L. H. Aung, J. L. Smilanick, P. V. Vail, P. L. Hartsell, and E. Gomez, "Investigations into the origin of chloroanisoles causing musty off-flavor of raisins," J. Agric. Food Chem. 44, 3294-3296 (1996).
[CrossRef]

J. Biosci. Bioeng. (1)

A. Miki, A. Isogai, H. Utsunomiya, and H. Iwata, "Identification of 2,4,6-trichloroanisole (TCA) causing a musty/muddy off-flavor in sake and its production in rice koji and moromi mash," J. Biosci. Bioeng. 100, 178-183 (2005).
[CrossRef] [PubMed]

J. Chem. Phys. (1)

D. S. Venables and C. A. Schmuttenmaer, "Spectroscopy and dynamics of mixtures of water with acetone, acetonitrile, and methanol," J. Chem. Phys. 113, 11222-11236 (2000).
[CrossRef]

J. Chromatogr. A (2)

R. Juanola, D. Subirà, V. Salvadó, J. A. Garcia Regueiro, and E. Anticó, "Evaluation of an extraction method in the determination of the 2,4,6-trichloroanisole content of tainted cork," J. Chromatogr. A 953, 207-214 (2002).
[CrossRef] [PubMed]

E. Lizarraga, Á. Irigoyen, V. Belsue, and E. González-Peñas, "Determination of chloroanisole compounds in red wine by headspace solid-phase microextraction and gas chromatography-mass spectrometry," J. Chromatogr. A 1052, 145-149 (2004).
[CrossRef] [PubMed]

J. Opt. Soc. Am. A (1)

J. Phys. Chem B (1)

M. C. Beard, G. M. Turner, and C. A. Schmuttenmaer, "THz spectroscopy," J. Phys. Chem B 106, 7146-7159 (2002).
[CrossRef]

Nucl. Instrum. Methods Phys. Res. B (1)

A. Brunetti, R. Cesareo, B. Golosio, P. Luciano, and A. Ruggero, "Cork quality estimation by using Compton tomography," Nucl. Instrum. Methods Phys. Res. B 196, 161-168 (2002).
[CrossRef]

Opt. Commun. (1)

T. Yasui, T. Yasuda, T. Araki, and E. Abraham, "Real-time two-dimensional terahertz tomography of moving objects," Opt. Commun. 267, 128-136 (2006).
[CrossRef]

Opt. Lett. (1)

Semicond. Sci. Technol. (1)

J. F. Federici, B. Schulkin, F. Huang, D. Gary, R. Barat, F. Oliveira, and D. Zimdars, "THz imaging and sensing for security applications-explosives, weapons and drugs," Semicond. Sci. Technol. 20, S266-S280 (2005).
[CrossRef]

Water Sci. Technol. (2)

A. Nystrom, A. Grimvall, C. Krantz-Rulcker, R. Savenhed, and K. Akerstrand, "Water off-flavour caused by 2,4,6-trichloroanisole," Water Sci. Technol. 25, 241-249 (1992).

S. Karlsson, S. Kaugare, A. Grimvall, H. Boren, and R. Savenhed, "Formation of 2,4,6-trichlorophenol and 2,4,6-trichloroanisole during treatment and distribution of drinking water," Water Sci. Technol. 31, 99-103 (1995).
[CrossRef]

Other (8)

Y. L. Hor, H. C. Lim, J. F. Federici, E. Moore, and J. W. Bozzelli, "Terahertz spectroscopy of trichloroanisole," (submitted to Chem. Phys. Lett.).

J. F. Federici, D. Gary, R. Barat, and Z.-H. Michalopoulou, "Detection of Explosives by Terahertz Imaging," in Counter-Terrorism Detection Techniques of Explosives, J. Yinon, ed. (Elsevier, 2007).
[CrossRef]

F. C. Delucia, "Spectroscopy in the terahertz spectral region," in Sensing with Terahertz Radiation, D. Mittleman ed. (Springer, 2003).

D. Mittleman, "Terahertz imaging," in Sensing with Terahertz Radiation, D. Mittleman, ed. (Springer, 2003).

E. Herve, S. Price, G. Burns, and P. Weber, presented at the ASEV Annual Meeting, Reno, Nevada, 2 July 1999. http://www.corkqc.com/asev/asev2-2.htm.

D. Zimdars, J. A. Valdmanis, J. S. White, G. Stuk, W. P. Winfree, and E. I. Madaras, "Time domain terahertz detection of flaws within space shuttle sprayed on foam insulation," in Conference on Lasers and Electro-Optics/(CLEO), Vol. 96 of OSA Trends in Optics and Photonics (Optical Society of America, 2004), paper CThN4. http://www.opticsinfobase.org/abstract.cfm?id=104293.

H. S. Chua, P. C. Upadhya, A. D. Haigh, J. Obradovic, A. A. P. Gibson, and E. H. Linfield, "Terahertz time-domain spectroscopy of wheat grain," in Conference Digest of the 2004 Joint 29th International Conference on Infrared and Millimeter Waves and 12th International Conference on Terahertz Electronics (IEEE, 2004), pp. 399-400.
[CrossRef]

H. S. Chua, J. Obradovic, A. D. Haigh, P. C. Upadhya, O. Hirsch, D. Crawley, A. A. P. Gibson, and E. H. Linfield, "Terahertz time-domain spectroscopy of crushed wheat grain," in 2005 IEEE MTT-S International Microwave Symposium (IEEE, 2005), p. 4.

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Figures (8)

Fig. 1
Fig. 1

(a) Measured THz time-domain waveform (gray) through a 4.4   mm thick cork sample. The reference waveform (black) is taken with the sample removed. (b) Corresponding amplitude as a function of frequency after Fourier transforming the time-domain data. Sharp structures near 0.57, 0.7, and 1.1   THz and other frequencies in the reference waveform are artifacts of absorption by water vapor in the atmosphere.

Fig. 2
Fig. 2

Calculated frequency dependent absorbance (black) and real index of refraction (gray) for the time-domain waveforms of Fig. 1.

Fig. 3
Fig. 3

(Color online) Front (a) and back visible (b) and 0.6 0.7   THz (c) image through a 4.4   mm cork sample. Each pixel is 500   μm . The front of the cork corresponds to the end that nominally would be in contact with the wine and the portion of the cork that could be visibly inspected. The visible image of the back side image is reversed left to right for easier comparison to the THz image. The sample is oriented so that the grains of the cork are parallel to the bottom of the page. The image ( 0.9 1 .0   THz transmission) of (d) is a high resolution ( 100   μm pixel) image of the area outlined in white.

Fig. 4
Fig. 4

(Color online) Front and back visible (left) and terahertz (right) images through a 4.35   mm (upper) sample from a different cork from Fig. 3. As with Fig. 3, note the presence of cracks, void, and cork grain that are visible in the terahertz image that otherwise would be overlooked in examining only the front visible image.

Fig. 5
Fig. 5

(Color online) Front and back visible (left) and THz (right) image through a 4.02   mm sample. This sample shows the image of hole (bright spot) and cavities (dark spot) that are visible in the THz image.

Fig. 6
Fig. 6

(Color online) THz transmission images in 0.1   THz bandwidths from 0.1 0.2   THz through 0.9 1 .0   THz (left to right, top to bottom progression). Note the improvement in spatial resolution with increasing THz frequency. Each pixel is 500   μm .

Fig. 7
Fig. 7

Absorption spectra (black) from pixel position ( x 37 , y 42 ) of Fig. 3 corresponding to a large crack∕void in the THz cork image. Note the presence of the sharp feature near 0.39   THz . Corresponding spectra (gray) from pixel position ( x 13 , y 51 ) corresponding to the edge of the cork. Note again the presence of an anomalous spectral peak near 0.47   THz .

Fig. 8
Fig. 8

Measured absorbance (upper black curve) from pixel position ( x 15 , y 34 ) of Fig. 3 (vertically offset by 1.0) corresponding to a dark grain in the cork THz image. Gray curve is a power law fit to the data using Eq. (3). Extracted parameters: C = 4.844 , m = 4.002 , B = 0.1636 . Bottom curve is the absorbance spectra from pixel position ( x 14 , y 32 ) corresponding to a clear grain in the cork THz image. Extracted parameters: C = 0.7924 , m = 1.126 , B = 0.09013 . The dashed curve (vertically offset by 0.5) is the predicted absorbance of 18 μm radius particles. The index of refraction is 1.1, sample thickness 4.4 m m , and the number of particles per volume is 2 × 10 13 m 3 . Fitting these curves to a power law dependence yields fitting parameters from Eq. (3) of A = 1.837 , m = 1.91 .

Tables (1)

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Table 1 Summary of Extracted Parameters from Power Law Dependence of Absorbance Spectra

Equations (8)

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A ( ν ) = ln ( T ( ν ) ) = ln ( | E s ( ν ) | / | E r ( ν ) | ) = μ L ,
n real ( ν ) = ( ϕ r ( ν ) ϕ s ( ν ) ) c 2 π ν L + 1 ,
A ( ν ) = C ν m + B ,
μ t h = N c 2 2 π ν 2 m = 1 ( 2 m + 1 ) Re ( a m + b m ) ,
a m = ψ m ( y ) ψ m ( x ) n ψ m ( y ) ψ m ( x ) ψ m ( y ) ζ m ( x ) n ψ m ( y ) ζ m ( x ) ,
b m = n ψ m ( y ) ψ m ( x ) ψ m ( y ) ψ m ( x ) n ψ m ( y ) ζ m ( x ) ψ m ( y ) ζ m ( x ) ,
ψ m ( z ) = z j m ( z ) ,
ζ m ( z ) = z h m ( 2 ) ( z ) .

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