Controlling light in scattering media non-invasively using the photoacoustic transmission matrix

Abstract

Optical wavefront shaping has emerged as a powerful tool for manipulating light in strongly scattering media. It enables diffraction-limited focusing and imaging at depths where conventional microscopy techniques fail. However, to date, most examples of wavefront shaping have relied on direct access to the targets or implanted probes, and the challenge is to apply it non-invasively inside complex samples. Recently, ultrasonic-tagging techniques have been utilized successfully, but these allow only small acoustically tagged volumes to be addressed at each measurement. Here, we introduce an approach that allows the non-invasive measurement of an optical transmission matrix over a large volume, inside complex samples, using a standard photoacoustic imaging set-up. We demonstrate the use of this matrix for detecting, localizing and selectively focusing light on absorbing targets through diffusive samples, as well as for extracting the scattering medium properties. Combining the transmission-matrix approach with the advantages of photoacoustic imaging opens a path towards deep-tissue imaging and light delivery utilizing endogenous optical contrast. An approach is demonstrated that allows the optical transmission matrix to be noninvasively measured over a large volume inside complex samples using a standard photoacoustic imaging set-up. This approach opens the way towards deep-tissue imaging and light delivery utilizing endogenous optical contrast.