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Published August 2011 | Published
Journal Article Open

Time-reversed ultrasonically encoded optical focusing into tissue-mimicking media with thickness up to 70 mean free paths


In turbid media such as biological tissue, multiple scattering hinders direct light focusing at depths beyond one transport mean free path. As a solution to this problem, time-reversed ultrasonically encoded (TRUE) optical focusing is proposed based on ultrasonic encoding of diffused laser light and optical time reversal. In TRUE focusing, a laser beam of long coherence length illuminates a turbid medium, where the incident light undergoes multiple scattering and part of it gets ultrasonically encoded within the ultrasonic focal zone. A conjugated wavefront of the ultrasonically encoded light is then generated by a phase conjugate mirror outside the medium, which traces back the trajectories of the ultrasonically encoded diffused light and converges light to the ultrasonic focal zone. Here, we report the latest experimental improvement in TRUE optical focusing that increases its penetration in tissue-mimicking media from a thickness of 3.75 to 7.00 mm. We also demonstrate that the TRUE focus depends on the focal diameter of the ultrasonic transducer.

Additional Information

© 2011 SPIE. Paper 11116R received Mar. 9, 2011; revised manuscript received Jun. 15, 2011; accepted for publication Jun. 17, 2011; published online Aug. 1, 2011. The authors appreciate Professor James Ballard's editing of the manuscript. This research is funded in part by the National Institutes of Health Grant Nos. R01 EB000712 and U54 CA136398.

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