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Focusing light into turbid media: time-reversed ultrasonically encoded (TRUE) focusing

Liu, Honglin and Xu, Xiao and Wang, Lihong V. (2011) Focusing light into turbid media: time-reversed ultrasonically encoded (TRUE) focusing. In: Photons Plus Ultrasound: Imaging and Sensing 2011. Proceedings of SPIE. No.7899. Society of Photo-optical Instrumentation Engineers (SPIE) , Bellingham, WA, Art. No. 78991A. ISBN 9780819484369.

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In turbid media such as biological tissues, light undergoes multiple scattering. Consequently, it is not possible to focus light at depths beyond one transport mean free path in such media. To break through this limit, we proposed and experimentally demonstrated a novel technique, based on ultrasonic encoding of diffused laser light and optical time reversal, which effectively focuses light into a turbid medium. In the experimental implementation of the Time-Reversed Ultrasonically Encoded (TRUE) optical focusing, a turbid medium was illuminated by a laser beam with a long coherence length. The incident light was multiply scattered inside the medium and ultrasonically encoded within the ultrasonic focal zone. The wavefront of the ultrasonically encoded light was then time reversed by a Phase Conjugate Mirror (PCM) outside the medium. The time-reversed (or phase conjugated) optical wavefront traced back the trajectories of the ultrasonically encoded diffused light, and converged to the ultrasonic focal zone. With a commercially available photorefractive crystal as the PCM, the main approaches for increasing focusing depth are to improve the efficiencies of ultrasonic encoding and time reversal. Our recent experiments showed that light can be focused into a 5-mm thick tissue-mimicking phantom (optical thickness = 50, i.e., geometric thickness = 50 mean free paths) with a dynamically adjustable focus. The TRUE optical focusing opens a door to focusing light into turbid media or manipulating light-matter interactions.

Item Type:Book Section
Related URLs:
URLURL TypeDescription
Liu, Honglin0000-0003-2473-9056
Wang, Lihong V.0000-0001-9783-4383
Additional Information:© 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). This research is funded in part by the National Institutes of Health grants R01 EB000712 and U54 CA136398.
Funding AgencyGrant Number
NIHR01 EB000712
NIHU54 CA136398
Subject Keywords:Ultrasound-modulated optical imaging, optical phase conjugation, optical time reversal, scattering medium, light manipulation
Series Name:Proceedings of SPIE
Issue or Number:7899
Record Number:CaltechAUTHORS:20180920-130934656
Persistent URL:
Official Citation:Honglin Liu, Honglin Liu, Xiao Xu, Xiao Xu, Lihong V. Wang, Lihong V. Wang, } "Focusing light into turbid media: time-reversed ultrasonically encoded (TRUE) focusing", Proc. SPIE 7899, Photons Plus Ultrasound: Imaging and Sensing 2011, 78991A (18 February 2011); doi: 10.1117/12.876956;
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:89803
Deposited By: George Porter
Deposited On:20 Sep 2018 22:39
Last Modified:09 Mar 2020 13:19

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