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Time-reversed ultrasonically encoded optical focusing into scattering media

Nature Photonics volume 5, pages 154–157 (2011)Cite this article

Abstract

Light focusing plays a central role in biomedical imaging, manipulation and therapy. In scattering media, direct light focusing becomes infeasible beyond one transport mean free path. All previous methods1,2,3 used to overcome this diffusion limit lack a practical internal ‘guide star’4. Here, we propose and experimentally validate a novel concept called time-reversed ultrasonically encoded (TRUE) optical focusing to deliver light into any dynamically defined location inside a scattering medium. First, diffused coherent light is encoded by a focused ultrasonic wave to provide a virtual internal guide star. Only the encoded light is time-reversed and transmitted back to the ultrasonic focus. The time-reversed ultrasonically encoded optical focus—defined by the ultrasonic wave—is unaffected by multiple scattering of light. Such focusing is particularly desirable in biological tissue, where ultrasonic scattering is ∼1,000 times weaker than optical scattering. Various fields, including biomedical and colloidal optics, can benefit from TRUE optical focusing.

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Figure 1: Schematic of the experimental setup for TRUE optical focusing.
Figure 2: Two-dimensional Monte Carlo simulation of light propagation inside a scattering slab with dimensions x = 160Ls and z = 40Ls.
Figure 3: Results from four imaging experiments validating TRUE optical focusing.

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Acknowledgements

This work was sponsored in part by the National Institutes of Health (grants R01 EB000712, R01 EB008085, R01 CA134539, U54 CA136398 and 5P60 DK02057933).

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Authors and Affiliations

  1. Department of Biomedical Engineering, Optical Imaging Laboratory, Washington University in St. Louis, St. Louis, 63130-4899, Missouri, USA

    Xiao Xu, Honglin Liu & Lihong V. Wang

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  1. Xiao Xu
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  2. Honglin Liu
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  3. Lihong V. Wang
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Contributions

X.X. and H.L. contributed equally to the experimental design and study, Monte Carlo simulation, data analysis and writing of the manuscript. L.V.W. conceived the original idea, discussed the experiments and revised the paper.

Corresponding author

Correspondence to Lihong V. Wang.

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Competing interests

The authors declare competing financial interests: L.V.W. has a financial interest in Microphotoacoustics and Endra, which, however, did not support this work.

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Xu, X., Liu, H. & Wang, L. Time-reversed ultrasonically encoded optical focusing into scattering media. Nature Photon 5, 154–157 (2011). https://doi.org/10.1038/nphoton.2010.306

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