Abstract

We have developed a laser speckle imaging method to reveal obscured subsurface inhomogeneities that cannot be seen under incoherent illumination. Speckle images of a scattering object were generated under coherent illumination using a laser. A sequence of speckle images was acquired with fixed exposure time and acquisition interval. The temporal statistics of each pixel in the image sequence was calculated and formed a new image. We demonstrate that such temporal speckle contrast images can reveal obscured subsurface objects. More importantly, by controlling image acquisition parameters, surface inhomogeneity can be eliminated in order to better bring to view the subsurface objects.

© 2005 Optical Society of America

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References

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Appl. Opt. (2)

J. Biomed. Opt. (2)

J. Li, G. Yao, L.H.V Wang, "Degree of polarization in laser speckles from turbid media: Implications in tissue optics," J. Biomed. Opt. 7, 307-312 (2002).
[CrossRef] [PubMed]

H. Cheng, Q. Luo, S. Zeng, S. Chen, J. Cen, and H. Gong, "Modified laser speckle imaging method with improved spatial resolution," J. Biomed. Opt. 8, 559-564 (2003).
[CrossRef] [PubMed]

Opt. Express (3)

Opt. Lasers Eng. (1)

M. Pajuelo, G. Baldwin, H. Rabal, N. Cap, R. Arizaga, M. Trivi, "Bio-speckle assessment of bruising in fruits," Opt. Lasers Eng. 40, 13-24 (2003).
[CrossRef]

Opt. Lett. (2)

Science (1)

L. Wang, P. P. Ho, G. Liu, G. Zhang, and R. R. Alfano, "Ballistic 2-D imaging through scattering wall using an ultrafast Kerr gate," Science 253, 769-771 (1991).
[CrossRef] [PubMed]

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Figures (5)

Fig. 1.
Fig. 1.

Schematic diagram of experimental setup.

Fig. 2.
Fig. 2.

Images of an obscured void hole underneath a white paper. Images listed in the 1st row were acquired with incoherent white light illumination; whereas imaged in the 2nd row were acquired using laser illumination.

Fig. 3.
Fig. 3.

Images of obscured black paint and white paint objects. (a) Incoherent image; (b) Temporal speckle contrast image.

Fig. 4.
Fig. 4.

Targets for examining the effect of image capture parameters. (a) Averaged speckle images; (b) Temporal speckle contrast image; (c) Image contrast changes with acquisition interval.

Fig. 5.
Fig. 5.

Images of a piece of paper with printed words on both sides. (a) Multiply-averaged laser image; (b) The standard-deviation image; (c) The temporal speckle contrast image. The images were horizontally flipped to display the obscured words on the back surface in readable order.

Equations (2)

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C i , j = 1 N 1 t = t 0 T ( X i , j t X ̅ i , j ) 2 X ̅ i , j
X ̅ i , j = 1 N t = t 0 T X i , j t

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