Abstract
The use of wavefront shaping to compensate for scattering has brought a renewed interest as a potential solution to imaging through scattering walls. A key to the practicality of any imaging through scattering technique is the capability to focus light without direct access behind the scattering wall. Here we address this problem using photoacoustic feedback for wavefront optimization. By combining the spatially non-uniform sensitivity of the ultrasound transducer to the generated photoacoustic waves with an evolutionary competition among optical modes, the speckle field develops a single, high intensity focus significantly smaller than the acoustic focus used for feedback. Notably, this method is not limited by the size of the absorber to form a sub-acoustic optical focus. We demonstrate imaging behind a scattering medium using two different imaging modalities with up to ten times improvement in signal-to-noise ratio and five to six times sub-acoustic resolution.
Highlights
The use of wavefront shaping to compensate for scattering has brought a renewed interest as a potential solution to imaging through scattering walls
Previous work using photoacoustic feedback with wavefront shaping has assumed that this feedback would create an optical focus limited by the size of the acoustic focus[16,17]
A focused ultrasound transducer displays a Gaussian spatial sensitivity, which essentially weights the photoacoustic response generated by the optical speckle; giving higher weighting to signals generated closer to the centre (Fig. 1c)
Summary
The use of wavefront shaping to compensate for scattering has brought a renewed interest as a potential solution to imaging through scattering walls. By combining the spatially non-uniform sensitivity of the ultrasound transducer to the generated photoacoustic waves with an evolutionary competition among optical modes, the speckle field develops a single, high intensity focus significantly smaller than the acoustic focus used for feedback. This method is not limited by the size of the absorber to form a sub-acoustic optical focus. The time reversal of variance encoded light approach was shown to break the acoustic resolution barrier by isolating the spatial location of optical speckles within the ultrasound focus While both of these techniques are promising for deep fluorescence imaging in scattering materials, their inherent low signal-to-noise ratio (SNR) could limit implementation. Such capabilities enable superb three-dimensional imaging of complex biological structures
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