Abstract

A common-path swept-source optical coherence tomography (SS-OCT) is a promising scheme for implementing a high-speed and stable OCT system. We investigate the capability of a common-path SS-OCT system to perform the cross-sectional imaging of valuable documents translated at high speed for the check of its security feature. The influence of transport speeds, up to 2000 mm/s, on the depth resolution and the signal intensity is experimentally evaluated using a SS-OCT system equipped with a swept source at a center wavelength of 1335 nm and with a sweep repetition rate of 50 kHz. The degradation of the measured signal is in good agreement with theory.

© 2011 Optical Society of America

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References

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  1. R. L. Van Renesse, Optical Document Security (Artech House, 2005).
  2. K. Fujiwara and O. Matoba, “Detection and evaluation of security features embedded in paper using spectral-domain optical coherence tomography,” Opt. Rev.18, 171–175 (2011).1340-6000
    [CrossRef]
  3. D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito, and J. G. Fujimoto, “Optical coherence tomography,” Science254, 1178–1181 (1991).0036-8075
    [CrossRef]
  4. Y. Cheng and K. Larin, “Artificial fingerprint recognition by using optical coherence tomography with autocorrelation analysis,” Appl. Opt.45, 9238–9245 (2006).0003-6935
    [CrossRef]
  5. Y. Hayasaki, Y. Matsuba, A. Nagaoka, H. Yamamoto, and N. Nishida, “Hiding an image with a light-scattering medium and use of a contrast-discrimination method for readout,” Appl. Opt.43, 1552–1558 (2004).0003-6935
    [CrossRef]
  6. E. Alarousu, L. Krehut, T. Prykari, and R. Myllyla, “Study on the use of optical coherence tomography in measurements of paper properties,” Meas. Sci. Technol.16, 1131–1137 (2005).0957-0233
    [CrossRef]
  7. T. Fabritius, E. Alarousa, T. Prykari, J. Hast, and R. Myllyla, “Characterisation of optically cleared paper by optical coherence tomography,” Quantum Electron.36, 181–187 (2006).1063-7818
    [CrossRef]
  8. M. J. Ju, S. J. Lee, E. J. Min, Y. Kim, H. Y. Kim, and B. H. Lee, “Evaluating and identifying pearls and their nuclei by using optical coherence tomography,” Opt. Express18, 13468–13477 (2010).1094-4087
    [CrossRef]
  9. R. Leitgeb, C. K. Hitzenberger, and A. F. Fercher, “Performance of fourier domain vs. time domain optical coherence tomography,” Opt. Express11, 889–894 (2003).1094-4087
    [CrossRef]
  10. J. F. de Boer, B. Cense, B. H. Park, M. C. Pierce, G. J. Tearney, and B. E. Bouma, “Improved signal-to-noise ratio in spectral-domain compared with time-domain optical coherence tomography,” Opt. Lett.28, 2067–2069 (2003).0146-9592
    [CrossRef]
  11. M. A. Choma, M. V. Sarunic, C. Yang, and J. A. Izatt, “Sensitivity advantage of swept source and Fourier domain optical coherence tomography,” Opt. Express11, 2183–2189 (2003).1094-4087
    [CrossRef]
  12. S. H. Yun, G. J. Tearney, J. F. de Boer, N. Iftimia, and B. E. Bouma, “High-speed optical frequency-domain imaging,” Opt. Express11, 2953–2963 (2003).1094-4087
    [CrossRef]
  13. A. B. Vakhtin, D. J. Kane, W. R. Wood, and K. A. Peterson, “Common-path interferometer for frequency-domain optical coherence tomography,” Appl. Opt.42, 6953–6958 (2003).0003-6935
    [CrossRef]
  14. K. M. Tan, M. Mazilu, T. H. Chow, W. M. Lee, K. Taguchi, B. K. Ng, W. Sibbett, C. S. Herrington, C. T. A. Brown, and K. Dholakia, “In-fiber common-path optical coherence tomography using a conical-tip fiber,” Opt. Express17, 2375–2384 (2009).1094-4087
    [CrossRef]
  15. A. F. Fercher, C. K. Hitzenberger, G. Kamp, and S. Y. Elzaiat, “Measurement of intraocular distances by backscattering spectral interferometry,” Opt. Commun.117, 43–48 (1995).0030-4018
    [CrossRef]
  16. M. Wojtkowski, V. J. Srinivasan, T. H. Ko, J. G. Fujimoto, A. Kowalczyk, and J. S. Duker, “Ultrahigh-resolution, high-speed, Fourier domain optical coherence tomography and methods for dispersion compensation,” Opt. Express12, 2404–2422 (2004).1094-4087
    [CrossRef]
  17. N. A. Nassif, B. Cense, B. H. Park, M. C. Pierce, S. H. Yun, B. E. Bouma, G. J. Tearney, T. C. Chen, and J. F. de Boer, “In vivo high-resolution video-rate spectral-domain optical coherence tomography of the human retina and optic nerve,” Opt. Express12, 367–376 (2004).1094-4087
    [CrossRef]
  18. S. R. Chinn, E. A. Swanson, and J. G. Fujimoto, “Optical coherence tomography using a frequency-tunable optical source,” Opt. Lett.22, 340–342 (1997).0146-9592
    [CrossRef]
  19. Y. Yasuno, V. D. Madjarova, S. Makita, M. Akiba, A. Morosawa, C. Chang, T. Sakai, K. Chan, M. Itoh, and T. Yatagai, “Three-dimensional and high-speed swept-source optical coherence tomography for in vivo investigation of human anterior eye segments,” Opt. Express13, 10652–10664 (2005).1094-4087
    [CrossRef]
  20. S. H. Yun, G. J. Tearney, J. F. de Boer, and B. E. Bouma, “Motion artifacts in optical coherence tomography with frequency-domain ranging,” Opt. Express12, 2977–2998 (2004).1094-4087
    [CrossRef]
  21. J. Carlsson, P. Hellentin, L. Malmqvist, A. Persson, W. Persson, and C-G. Wahlstrom, “Time-resolved studies of light propagation in paper,” Appl. Opt.34, 1528–1535 (1995).0003-6935
    [CrossRef]
  22. K. Green, L. Lamberg, and K. Lumme, “Stochastic modeling of paper structure and Monte Carlo simulation of light scattering,” Appl. Opt.39, 4669–4683 (2000).0003-6935
    [CrossRef]
  23. M. Gora, K. Karnowski, M. Szkulmowski, B. J. Kaluzny, R. Huber, A. Kowalczyk, and M. Wojtkowski, “Ultra high-speed swept source OCT imaging of the anterior segment of human eye at 200 kHz with adjustable imaging range,” Opt. Express17, 14880–14894 (2009).1094-4087
  24. C. M. Eigenwilling, B. R. Biedermann, W. Wieser, and R. Huber, “Wavelength swept amplified spontaneous emission source,” Opt. Express17, 18794–18807 (2009).1094-4087
    [CrossRef]
  25. C. Blatter, B. Grajciar, C. M. Eigenwillig, W. Wieser, B. R. Biedermann, R. Huber, and R. A. Leitgeb, “Extended focus high-speed swept source OCT with self-reconstructive illumination,” Opt. Express19, 12141–12155 (2011).1094-4087
    [CrossRef]

2011 (2)

K. Fujiwara and O. Matoba, “Detection and evaluation of security features embedded in paper using spectral-domain optical coherence tomography,” Opt. Rev.18, 171–175 (2011).1340-6000
[CrossRef]

C. Blatter, B. Grajciar, C. M. Eigenwillig, W. Wieser, B. R. Biedermann, R. Huber, and R. A. Leitgeb, “Extended focus high-speed swept source OCT with self-reconstructive illumination,” Opt. Express19, 12141–12155 (2011).1094-4087
[CrossRef]

2010 (1)

2009 (3)

2006 (2)

T. Fabritius, E. Alarousa, T. Prykari, J. Hast, and R. Myllyla, “Characterisation of optically cleared paper by optical coherence tomography,” Quantum Electron.36, 181–187 (2006).1063-7818
[CrossRef]

Y. Cheng and K. Larin, “Artificial fingerprint recognition by using optical coherence tomography with autocorrelation analysis,” Appl. Opt.45, 9238–9245 (2006).0003-6935
[CrossRef]

2005 (2)

2004 (4)

2003 (5)

2000 (1)

1997 (1)

1995 (2)

J. Carlsson, P. Hellentin, L. Malmqvist, A. Persson, W. Persson, and C-G. Wahlstrom, “Time-resolved studies of light propagation in paper,” Appl. Opt.34, 1528–1535 (1995).0003-6935
[CrossRef]

A. F. Fercher, C. K. Hitzenberger, G. Kamp, and S. Y. Elzaiat, “Measurement of intraocular distances by backscattering spectral interferometry,” Opt. Commun.117, 43–48 (1995).0030-4018
[CrossRef]

1991 (1)

D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito, and J. G. Fujimoto, “Optical coherence tomography,” Science254, 1178–1181 (1991).0036-8075
[CrossRef]

Akiba, M.

Alarousa, E.

T. Fabritius, E. Alarousa, T. Prykari, J. Hast, and R. Myllyla, “Characterisation of optically cleared paper by optical coherence tomography,” Quantum Electron.36, 181–187 (2006).1063-7818
[CrossRef]

Alarousu, E.

E. Alarousu, L. Krehut, T. Prykari, and R. Myllyla, “Study on the use of optical coherence tomography in measurements of paper properties,” Meas. Sci. Technol.16, 1131–1137 (2005).0957-0233
[CrossRef]

Biedermann, B. R.

Blatter, C.

Bouma, B. E.

Brown, C. T. A.

Carlsson, J.

Cense, B.

Chan, K.

Chang, C.

Chang, W.

D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito, and J. G. Fujimoto, “Optical coherence tomography,” Science254, 1178–1181 (1991).0036-8075
[CrossRef]

Chen, T. C.

Cheng, Y.

Chinn, S. R.

Choma, M. A.

Chow, T. H.

de Boer, J. F.

Dholakia, K.

Duker, J. S.

Eigenwillig, C. M.

Eigenwilling, C. M.

Elzaiat, S. Y.

A. F. Fercher, C. K. Hitzenberger, G. Kamp, and S. Y. Elzaiat, “Measurement of intraocular distances by backscattering spectral interferometry,” Opt. Commun.117, 43–48 (1995).0030-4018
[CrossRef]

Fabritius, T.

T. Fabritius, E. Alarousa, T. Prykari, J. Hast, and R. Myllyla, “Characterisation of optically cleared paper by optical coherence tomography,” Quantum Electron.36, 181–187 (2006).1063-7818
[CrossRef]

Fercher, A. F.

R. Leitgeb, C. K. Hitzenberger, and A. F. Fercher, “Performance of fourier domain vs. time domain optical coherence tomography,” Opt. Express11, 889–894 (2003).1094-4087
[CrossRef]

A. F. Fercher, C. K. Hitzenberger, G. Kamp, and S. Y. Elzaiat, “Measurement of intraocular distances by backscattering spectral interferometry,” Opt. Commun.117, 43–48 (1995).0030-4018
[CrossRef]

Flotte, T.

D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito, and J. G. Fujimoto, “Optical coherence tomography,” Science254, 1178–1181 (1991).0036-8075
[CrossRef]

Fujimoto, J. G.

Fujiwara, K.

K. Fujiwara and O. Matoba, “Detection and evaluation of security features embedded in paper using spectral-domain optical coherence tomography,” Opt. Rev.18, 171–175 (2011).1340-6000
[CrossRef]

Gora, M.

Grajciar, B.

Green, K.

Gregory, K.

D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito, and J. G. Fujimoto, “Optical coherence tomography,” Science254, 1178–1181 (1991).0036-8075
[CrossRef]

Hast, J.

T. Fabritius, E. Alarousa, T. Prykari, J. Hast, and R. Myllyla, “Characterisation of optically cleared paper by optical coherence tomography,” Quantum Electron.36, 181–187 (2006).1063-7818
[CrossRef]

Hayasaki, Y.

Hee, M. R.

D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito, and J. G. Fujimoto, “Optical coherence tomography,” Science254, 1178–1181 (1991).0036-8075
[CrossRef]

Hellentin, P.

Herrington, C. S.

Hitzenberger, C. K.

R. Leitgeb, C. K. Hitzenberger, and A. F. Fercher, “Performance of fourier domain vs. time domain optical coherence tomography,” Opt. Express11, 889–894 (2003).1094-4087
[CrossRef]

A. F. Fercher, C. K. Hitzenberger, G. Kamp, and S. Y. Elzaiat, “Measurement of intraocular distances by backscattering spectral interferometry,” Opt. Commun.117, 43–48 (1995).0030-4018
[CrossRef]

Huang, D.

D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito, and J. G. Fujimoto, “Optical coherence tomography,” Science254, 1178–1181 (1991).0036-8075
[CrossRef]

Huber, R.

Iftimia, N.

Itoh, M.

Izatt, J. A.

Ju, M. J.

Kaluzny, B. J.

Kamp, G.

A. F. Fercher, C. K. Hitzenberger, G. Kamp, and S. Y. Elzaiat, “Measurement of intraocular distances by backscattering spectral interferometry,” Opt. Commun.117, 43–48 (1995).0030-4018
[CrossRef]

Kane, D. J.

Karnowski, K.

Kim, H. Y.

Kim, Y.

Ko, T. H.

Kowalczyk, A.

Krehut, L.

E. Alarousu, L. Krehut, T. Prykari, and R. Myllyla, “Study on the use of optical coherence tomography in measurements of paper properties,” Meas. Sci. Technol.16, 1131–1137 (2005).0957-0233
[CrossRef]

Lamberg, L.

Larin, K.

Lee, B. H.

Lee, S. J.

Lee, W. M.

Leitgeb, R.

Leitgeb, R. A.

Lin, C. P.

D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito, and J. G. Fujimoto, “Optical coherence tomography,” Science254, 1178–1181 (1991).0036-8075
[CrossRef]

Lumme, K.

Madjarova, V. D.

Makita, S.

Malmqvist, L.

Matoba, O.

K. Fujiwara and O. Matoba, “Detection and evaluation of security features embedded in paper using spectral-domain optical coherence tomography,” Opt. Rev.18, 171–175 (2011).1340-6000
[CrossRef]

Matsuba, Y.

Mazilu, M.

Min, E. J.

Morosawa, A.

Myllyla, R.

T. Fabritius, E. Alarousa, T. Prykari, J. Hast, and R. Myllyla, “Characterisation of optically cleared paper by optical coherence tomography,” Quantum Electron.36, 181–187 (2006).1063-7818
[CrossRef]

E. Alarousu, L. Krehut, T. Prykari, and R. Myllyla, “Study on the use of optical coherence tomography in measurements of paper properties,” Meas. Sci. Technol.16, 1131–1137 (2005).0957-0233
[CrossRef]

Nagaoka, A.

Nassif, N. A.

Ng, B. K.

Nishida, N.

Park, B. H.

Persson, A.

Persson, W.

Peterson, K. A.

Pierce, M. C.

Prykari, T.

T. Fabritius, E. Alarousa, T. Prykari, J. Hast, and R. Myllyla, “Characterisation of optically cleared paper by optical coherence tomography,” Quantum Electron.36, 181–187 (2006).1063-7818
[CrossRef]

E. Alarousu, L. Krehut, T. Prykari, and R. Myllyla, “Study on the use of optical coherence tomography in measurements of paper properties,” Meas. Sci. Technol.16, 1131–1137 (2005).0957-0233
[CrossRef]

Puliafito, C. A.

D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito, and J. G. Fujimoto, “Optical coherence tomography,” Science254, 1178–1181 (1991).0036-8075
[CrossRef]

Sakai, T.

Sarunic, M. V.

Schuman, J. S.

D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito, and J. G. Fujimoto, “Optical coherence tomography,” Science254, 1178–1181 (1991).0036-8075
[CrossRef]

Sibbett, W.

Srinivasan, V. J.

Stinson, W. G.

D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito, and J. G. Fujimoto, “Optical coherence tomography,” Science254, 1178–1181 (1991).0036-8075
[CrossRef]

Swanson, E. A.

S. R. Chinn, E. A. Swanson, and J. G. Fujimoto, “Optical coherence tomography using a frequency-tunable optical source,” Opt. Lett.22, 340–342 (1997).0146-9592
[CrossRef]

D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito, and J. G. Fujimoto, “Optical coherence tomography,” Science254, 1178–1181 (1991).0036-8075
[CrossRef]

Szkulmowski, M.

Taguchi, K.

Tan, K. M.

Tearney, G. J.

Vakhtin, A. B.

Van Renesse, R. L.

R. L. Van Renesse, Optical Document Security (Artech House, 2005).

Wahlstrom, C-G.

Wieser, W.

Wojtkowski, M.

Wood, W. R.

Yamamoto, H.

Yang, C.

Yasuno, Y.

Yatagai, T.

Yun, S. H.

Appl. Opt. (5)

Meas. Sci. Technol. (1)

E. Alarousu, L. Krehut, T. Prykari, and R. Myllyla, “Study on the use of optical coherence tomography in measurements of paper properties,” Meas. Sci. Technol.16, 1131–1137 (2005).0957-0233
[CrossRef]

Opt. Commun. (1)

A. F. Fercher, C. K. Hitzenberger, G. Kamp, and S. Y. Elzaiat, “Measurement of intraocular distances by backscattering spectral interferometry,” Opt. Commun.117, 43–48 (1995).0030-4018
[CrossRef]

Opt. Express (12)

M. Wojtkowski, V. J. Srinivasan, T. H. Ko, J. G. Fujimoto, A. Kowalczyk, and J. S. Duker, “Ultrahigh-resolution, high-speed, Fourier domain optical coherence tomography and methods for dispersion compensation,” Opt. Express12, 2404–2422 (2004).1094-4087
[CrossRef]

N. A. Nassif, B. Cense, B. H. Park, M. C. Pierce, S. H. Yun, B. E. Bouma, G. J. Tearney, T. C. Chen, and J. F. de Boer, “In vivo high-resolution video-rate spectral-domain optical coherence tomography of the human retina and optic nerve,” Opt. Express12, 367–376 (2004).1094-4087
[CrossRef]

K. M. Tan, M. Mazilu, T. H. Chow, W. M. Lee, K. Taguchi, B. K. Ng, W. Sibbett, C. S. Herrington, C. T. A. Brown, and K. Dholakia, “In-fiber common-path optical coherence tomography using a conical-tip fiber,” Opt. Express17, 2375–2384 (2009).1094-4087
[CrossRef]

M. A. Choma, M. V. Sarunic, C. Yang, and J. A. Izatt, “Sensitivity advantage of swept source and Fourier domain optical coherence tomography,” Opt. Express11, 2183–2189 (2003).1094-4087
[CrossRef]

S. H. Yun, G. J. Tearney, J. F. de Boer, N. Iftimia, and B. E. Bouma, “High-speed optical frequency-domain imaging,” Opt. Express11, 2953–2963 (2003).1094-4087
[CrossRef]

M. J. Ju, S. J. Lee, E. J. Min, Y. Kim, H. Y. Kim, and B. H. Lee, “Evaluating and identifying pearls and their nuclei by using optical coherence tomography,” Opt. Express18, 13468–13477 (2010).1094-4087
[CrossRef]

R. Leitgeb, C. K. Hitzenberger, and A. F. Fercher, “Performance of fourier domain vs. time domain optical coherence tomography,” Opt. Express11, 889–894 (2003).1094-4087
[CrossRef]

M. Gora, K. Karnowski, M. Szkulmowski, B. J. Kaluzny, R. Huber, A. Kowalczyk, and M. Wojtkowski, “Ultra high-speed swept source OCT imaging of the anterior segment of human eye at 200 kHz with adjustable imaging range,” Opt. Express17, 14880–14894 (2009).1094-4087

C. M. Eigenwilling, B. R. Biedermann, W. Wieser, and R. Huber, “Wavelength swept amplified spontaneous emission source,” Opt. Express17, 18794–18807 (2009).1094-4087
[CrossRef]

C. Blatter, B. Grajciar, C. M. Eigenwillig, W. Wieser, B. R. Biedermann, R. Huber, and R. A. Leitgeb, “Extended focus high-speed swept source OCT with self-reconstructive illumination,” Opt. Express19, 12141–12155 (2011).1094-4087
[CrossRef]

Y. Yasuno, V. D. Madjarova, S. Makita, M. Akiba, A. Morosawa, C. Chang, T. Sakai, K. Chan, M. Itoh, and T. Yatagai, “Three-dimensional and high-speed swept-source optical coherence tomography for in vivo investigation of human anterior eye segments,” Opt. Express13, 10652–10664 (2005).1094-4087
[CrossRef]

S. H. Yun, G. J. Tearney, J. F. de Boer, and B. E. Bouma, “Motion artifacts in optical coherence tomography with frequency-domain ranging,” Opt. Express12, 2977–2998 (2004).1094-4087
[CrossRef]

Opt. Lett. (2)

Opt. Rev. (1)

K. Fujiwara and O. Matoba, “Detection and evaluation of security features embedded in paper using spectral-domain optical coherence tomography,” Opt. Rev.18, 171–175 (2011).1340-6000
[CrossRef]

Quantum Electron. (1)

T. Fabritius, E. Alarousa, T. Prykari, J. Hast, and R. Myllyla, “Characterisation of optically cleared paper by optical coherence tomography,” Quantum Electron.36, 181–187 (2006).1063-7818
[CrossRef]

Science (1)

D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito, and J. G. Fujimoto, “Optical coherence tomography,” Science254, 1178–1181 (1991).0036-8075
[CrossRef]

Other (1)

R. L. Van Renesse, Optical Document Security (Artech House, 2005).

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Figures (6)

Fig. 1.
Fig. 1.

Optical setup of our common-path SS-OCT: L1, collimator lens; BS, cubic beam splitter; L2, objective lens; L3, focusing lens; GP, glass plate; PD, InGaAs photodetector; DAQ, data acquisition board; PC, personal computer. The back surface of GP serves as reference mirror.

Fig. 2.
Fig. 2.

Photograph of the common-path interferometer we have assembled for this work.

Fig. 3.
Fig. 3.

Point spread function (PSF) measured from a gold mirror placed at a distance of approximately 1.5 mm from the back surface of the glass plate GP. The FWHM depth resolution was determined to be 14.6 μm in air.

Fig. 4.
Fig. 4.

Cross-sectional OCT images of a valuable document embedded with a security thread acquired at six different sample translation motion speeds of (a) 10 mm/s, (b) 100 mm/s, (c) 250 mm/s, (d) 500 mm/s, (e) 1000 mm/s, and (f) 2000 mm/s. Each image is 6.0mm×0.4mm (transverse×depth) in size and displayed using a logarithmic gray-scale ranging from 15 to 40dB in intensity. The vertical scale of the images is plotted in optical depth. The security thread is embedded at a geometrical depth of approximately 40 μm below the front surface of the valuable document.

Fig. 5.
Fig. 5.

Averaged depth profiles obtained by averaging all A-scan profiles of each cross-sectional image shown in Fig. 4 along the transverse direction. The first peak (peak1) and the second peak (peak2) correspond to the front surface of the sample and the embedded security thread, respectively.

Fig. 6.
Fig. 6.

The relation between image quality and the sample translation motion speed. (a) The mean values of FWHM depth resolutions (circles for peak1, squares for peak2) determined from 10 averaged depth profiles measured at different transverse areas on the same sample for each translation motion speed. The solid line is a theoretical curve based on Eq. (1). (b) The mean values of the signal decreases (circles for peak1, squares for peak2) measured from the 10 average depth profiles. The solid line represents a theoretical curve based on Eq. (3) with a fitting factor of α=0.54.

Equations (3)

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δzδz0=1+(σvxTw0)2,
wxw0=1+(σvxTw0)2,
SNRdecrease[1+(σvxTw0)2]α,

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