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Bit-efficient sub-millisecond wavefront measurement using a lock-in camera for time-reversal based optical focusing inside scattering media

Liu, Yan and Ma, Cheng and Shen, Yuecheng and Wang, Lihong V. (2016) Bit-efficient sub-millisecond wavefront measurement using a lock-in camera for time-reversal based optical focusing inside scattering media. In: Adaptive Optics and Wavefront Control for Biological Systems II. Proceedings of SPIE. No.9717. Society of Photo-Optical Instrumentation Engineers , Bellingham, WA, Art. No. 97171J. ISBN 9781628419511. http://resolver.caltech.edu/CaltechAUTHORS:20180907-104553931

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Abstract

Optical focusing plays a central role in biomedical optical imaging, manipulation, and therapy. However, in scattering media, direct optical focusing becomes infeasible beyond ~10 mean free paths. To break this limit, time-reversed ultrasonically encoded (TRUE) optical focusing phase-conjugates ultrasonically tagged diffuse light back to the ultrasonic focus, thus forming a focus deep inside scattering media. In previous works, the speed of wavefront measurement was limited by the low frame rate of the camera used to record the four images required for phase-shifting holography. Moreover, most of the bits of a pixel value were used to represent an informationless background caused by the large amount of untagged light, increasing the amount of data to transfer and necessitating the use of costly high-resolution analog-to-digital converters (ADCs). Here, we developed a digital TRUE focusing system based on a lock-in camera (300×300 pixels), in which each pixel performs analog lock-in detection on chip. Since only the information of the signal, not that of the background, is digitized, the lock-in camera reduces the amount of data to transfer, and enables the use of cheap low-resolution ADCs. Using this lock-in camera, we were able to measure the wavefront of ultrasonically tagged light in less than 0.3 ms, and to achieve TRUE focusing in between two ground glass diffusers. Even when the signal-to-background ratio dropped to 6.32×10^(-4), a phase sensitivity as low as 0.51 rad could still be realized, which is more than enough for digital optical phase conjugation.


Item Type:Book Section
Related URLs:
URLURL TypeDescription
https://doi.org/10.1117/12.2211936DOIArticle
ORCID:
AuthorORCID
Shen, Yuecheng0000-0003-1990-8142
Wang, Lihong V.0000-0001-9783-4383
Additional Information:© 2016 Society of Photo-Optical Instrumentation Engineers.
Record Number:CaltechAUTHORS:20180907-104553931
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20180907-104553931
Official Citation:Yan Liu, Yan Liu, Cheng Ma, Cheng Ma, Yuecheng Shen, Yuecheng Shen, Lihong V. Wang, Lihong V. Wang, } "Bit-efficient sub-millisecond wavefront measurement using a lock-in camera for time-reversal based optical focusing inside scattering media (Conference Presentation)", Proc. SPIE 9717, Adaptive Optics and Wavefront Control for Biological Systems II, 97171J (27 April 2016); doi: 10.1117/12.2211936; https://doi.org/10.1117/12.2211936
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:89461
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:10 Sep 2018 19:51
Last Modified:10 Sep 2018 19:51

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