The main obstacle for optical imaging deep inside biological tissues is light scattering. Recently, three-photon (3p) microscopy extended the accessible depth ranges of fluorescence imaging due to its enhanced nonlinearity. On a different front, advances in optical wavefront shaping showed that scattering can be compensated for, even in regimes where light entirely lost its directionality. Combining these two approaches, we demonstrate focusing and imaging behind scattering layers, enabled through wavefront shaping guided by 3p fluorescence in situations where no ballistic light reaches the sample. We analyse different sample geometries and compare these results to the case of 2p excitation.
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