  Wavefront-shaping is a promising approach for imaging fluorescent targets
deep inside scattering tissue despite strong aberrations. It enables focusing
an incoming illumination into a single spot inside tissue, as well as
correcting the outgoing light scattered from the tissue, by modulating the
incoming and/or outgoing wavefronts. Previously, wavefront shaping modulations
have been successively estimated using feedback from strong fluorescent beads,
which have been manually added to a sample. However, ideally, such feedback
should be provided by the fluorescent components of the tissue itself, whose
emission is orders of magnitude weaker than the one provided by beads. When a
low number of photons is spread over multiple sensor pixels, the image is
highly susceptible to noise, and the feedback signal required for previous
algorithms cannot be detected. In this work, we suggest a wavefront shaping
approach that works with a confocal modulation of both the illumination and
imaging arms. Since the aberrations are corrected in the optics before the
detector, the low photon budget can be directed into a single sensor spot and
detected with high SNR. We derive a score function for modulation evaluation
from mathematical principles, and successfully use it to image EGFP labeled
neurons, despite scattering through thick tissue.
