  Optical wavefront-shaping has emerged as a powerful tool to manipulate light
in strongly scattering media. It enables diffraction-limited focusing and
imaging at depths where conventional microscopy techniques fail. However, while
most wavefront-shaping works to-date exploited direct access to the target or
implanted probes, the challenge is to apply it non-invasively inside complex
samples. Ultrasonic-tagging techniques have been recently demonstrated but
these require a sequential point-by- point acquisition, a major drawback for
imaging applications. Here, we introduce a novel approach to non-invasively
measure the optical transmission-matrix inside a scattering medium, exploiting
the photo-acoustic effect. Our approach allows for the first time to
simultaneously discriminate, localize, and selectively focus light on multiple
targets inside a scattering sample, as well as to recover and exploit the
scattering medium properties. Combining the powerful approach of the
transmission-matrix with the advantages of photoacoustic imaging opens the path
towards deep-tissue imaging and light-delivery utilizing endogenous optical
contrast.
