  Acousto-optic tomography (AOT) enables optical-contrast imaging deep inside
scattering samples via localized ultrasound modulation of scattered light.
However, the resolution of AOT is inherently limited by the ultrasound focus
size, prohibiting microscopic investigations. In the last few years, advances
in the field of digital wavefront-shaping have allowed the development of novel
approaches for overcoming the acoustic resolution limit of AOT. However, these
novel approaches require the execution of 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 AOT 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), originally developed for imaging blinking
fluorophores, to AOT. We show that naturally fluctuating optical speckle grains
can serve as the analogues of blinking fluorophores, enabling super-resolution
by statistical analysis of fluctuating acousto-optic signals.

Optics