  Over the past decade, optical wavefront shaping has been developed to focus
light through highly opaque scattering layers, opening new possibilities for
biomedical applications. To probe light intensity deep inside soft scattering
media such as biological tissues, internal guide-stars are required. Here, we
give an overview of the main principles and describe in depth the use of a
photoacoustic feedback signal for this purpose. We further present first
principles calculations and simulations to estimate important experimental
parameters, and detailed instructions on designing and conducting these
experiments. Finally, we provide guidance towards selecting suitable equipment
for building a typical experimental setup, paving the way for further
innovative biomedical imaging and therapy applications.
