Abstract
Acousto-optic imaging (AOI) enables optical-contrast imaging deep inside scattering samples via localized ultrasound modulation of scattered light. However, the resolution in AOI is inherently limited by the ultrasound focus size, prohibiting microscopic investigations. In recent years advances in the field of digital wavefront-shaping allowed the development of novel approaches for overcoming AOI’s acoustic resolution limit. However, these approaches require thousands of wavefront measurements within the sample speckle decorrelation time, limiting their application to static samples. Here, we show that it is possible to surpass the acoustic resolution-limit with a conventional AOI system by exploiting the natural dynamics of speckle decorrelations rather than trying to overcome them. We achieve this by adapting the principles of super-resolution optical fluctuations imaging (SOFI) to AOI. We show that naturally fluctuating optical speckle grains can serve in AOI as the analogues of blinking fluorophores in SOFI, enabling super-resolution by statistical analysis of fluctuating acousto-optic signals.
Highlights
Acousto-optic imaging (AOI) enables optical-contrast imaging deep inside scattering samples via localized ultrasound modulation of scattered light
AOI and photo-acoustic tomography (PAT) both provide images of optical contrast with a spatial resolution limited by the dimensions of the ultrasound focus, which is dictated by acoustic diffraction
We show that a superresolved AOI image can be obtained by statistical analysis of temporal fluctuations of ultrasonically modulated light, recorded using a conventional AOI setup
Summary
Acousto-optic imaging (AOI) enables optical-contrast imaging deep inside scattering samples via localized ultrasound modulation of scattered light. In PAT, nonlinear effects[8], dynamic speckle illumination[9,10], temporal fluctuations from flowing absorbers[11], or localization of isolated absorbers[12,13] were exploited to provide sub-acoustic resolution Recent approaches that rely on optical wavefront-shaping to focus light into the acoustic focus, can surpass the acoustic diffraction limit via either digital phase-conjugation[15,16], or by measurement of the acousto-optic transmission matrix[17] These novel wavefrontshaping based approaches require a very large number of measurements (up to several thousands16,17) and digital wavefrontshaped illumination to take place within the speckle decorrelation time of the sample. Our approach allows to perform superresolved AOI with speckle decorrelation times orders of magnitude shorter than current approaches
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