  Full-field imaging through scattering media is fraught with many challenges.
Despite many achievements in recent years, current imaging methods are too slow
to deal with fast dynamics that occur for example in biomedical imaging. Here
we present an ultra-fast all-optical method, where the object to be imaged and
the scattering medium (diffuser) are inserted into a highly multimode
self-imaging laser cavity. We show that the intra-cavity laser light from the
object is mainly focused onto specific regions of the scattering medium where
the phase variations are low. Thus, round trip loss within the laser cavity is
minimized, thereby overcoming most of the scattering effects. The method is
exploited to image objects through scattering media whose diffusion angle is
lower than the numerical aperture of the laser cavity. As our method is based
on optical feedback inside a laser cavity, it can deal with temporal variations
that occur on timescales as short as several cavity round trips, with an upper
bound of 200 ns.
