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Published April 1, 2016 | Published
Journal Article Open

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


Time-reversed ultrasonically encoded optical focusing measures the wavefront of ultrasonically tagged light, and then phase conjugates the tagged light back to the ultrasonic focus, thus focusing light deep inside the scattering media. In previous works, the speed of wavefront measurement was limited by the low frame rates of conventional cameras. In addition, these cameras used most of their bits to represent an informationless background when the signal-to-background ratio was low, resulting in extremely low efficiencies in the use of bits. Here, using a lock-in camera, we increase the bit efficiency and reduce the data transfer load by digitizing only the signal after rejecting the background. With this camera, we obtained the wavefront of ultrasonically tagged light after a single frame of measurement taken within 0.3 ms, and focused light in between two diffusers. The phase sensitivity has reached 0.51 rad even when the SBR is 6×10^(−4).

Additional Information

© 2016 Optical Society of America. Received 13 October 2015; revised 25 January 2016; accepted 8 February 2016; posted 10 February 2016 (Doc. ID 251850); published 16 March 2016. Funding: National Institutes of Health (NIH) (DP1 EB016986, R01 CA186567).

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