Applied Physics

TRUE Vision

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Science  04 Feb 2011:
Vol. 331, Issue 6017, pp. 513
DOI: 10.1126/science.331.6017.513-b

Optical imaging within biological tissue has to overcome the problem of multiple scattering events. Xu et al. show how to encode optical laser light with ultrasonic frequencies so that it effectively focuses to a point despite scattering. They split the light into three components: two reference beams and a sample beam. The latter is sent though two acousto-optic modulators to add ultrasonic-frequency side bands, allowing a focal point to be created in the scattering medium with ultrasound, which scatters about a thousandth as strongly as optical light. The light from the sample is collected in a photorefractive crystal as a hologram with the use of the reference beams, and then read out to create a time-reversed image; only the light that was encoded with ultrasound is unaffected by multiple scattering. These time-reversed ultrasonically encoded, or TRUE images, have a resolution determined by the ultrasonic frequency, in this case, 0.63 mm for light with a wavelength of 532 nm.

Nat. Photon. 5, 10.1038/NPHOTON.2010.306 (2011).

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