optical focusing in biological tissue

We report an experimental investigation of time- reversed ultrasonically encoded optical focusing in biologi- cal tissue. This technology combines the concepts of optical phase conjugation and ultrasound modulation of diffused coherent light. The ultrasonically encoded (or tagged) dif- fused light from a tissue sample is collected in reflection mode and interferes with a reference light in a photorefrac- tive crystal (used as a phase conjugation mirror) to form a hologram. Then a time-reversed copy of the tagged light is generated and traces back the original trajectories to the ultrasonic focus inside the tissue sample. With our current setup, we can achieve a maximum penetration depth of 5 mm in a chicken breast sample and image optical contrasts within a tissue sample with a spatial resolution approximately equaling 1∕ ffiffiffi p of the ultrasound focal diameter. © 2012 Society of Photo-Optical Instrumentation Engineers

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