Sub-acoustic resolution photoacoustic imaging through scattering layers using speckle correlations
Optical scattering presents a major obstacle to high resolution imaging in biological tissue and other turbid media. Conventional photoacoustic imaging can partially overcome this obstacle, enabling imaging of optical absorption in the multiple-scattering regime, but its resolution remains limited by acoustic diffraction. In this work we explore a strategy to overcome this limit by exploiting correlations in the illumination patterns produced by coherent scattered light. Combining controlled speckle translations with photoacoustic signal detection, this method enables the recovery of optical resolution images within acoustically selected regions, while overcoming the strict decorrelation range limitations of other speckle correlation techniques. In proof-of-concept experiments, we demonstrate imaging of objects hidden behind an opaque diffuser at sub-acoustic diffraction limited (<11um) resolution, over a >5mm^2 field of view much larger than the effective speckle decorrelation range. These results suggest that speckle correlation based photoacoustic imaging may offer a route to high resolution imaging of optical absorption under scattering conditions where conventional optical or photoacoustic techniques are fundamentally limited.