Light-sheet microscopy, such as ultramicroscopy, single plane illumination microscopy (SPIM)  and digital
scanned laser microscopy (DSLM) , represents a useful tool for biological investigations of thick samples.
Such techniques have been found particularly useful in developmental biology applications since they provide the
capability to perform fast imaging of living samples reducing photobleaching effects. The high signal to noise ratio
and the intrinsic optical sectioning capability provided by SPIM suggest this technique as the best choice for
imaging of thick scattering samples. Nevertheless, imaging in depth of large samples suffers from a decreasing in
the image quality due to scattering effects. Two photon excitation microscopy  became a popular tool to perform
imaging in turbid media since it improves the penetration depth capability and it reduces the image quality
degradation due to scattering  and light matter interactions. Therefore, two photon excitation within the light
sheet illumination scheme has been exploited in order to reduce scattering effects due to light-sample interactions. In
this work two photon excitation imaging in SPIM scheme has been performed in order to achieve an improvement
in the penetration depth while imaging living biological samples.
Non linear optical scanning microscopy has became a useful tool for living tissue imaging. Biological tissues
are highly scattering media and this leads to an exponential attenuation of the excitation intensity as the light
travels into the sample. While performing imaging of biological scattering tissues in non linear excitation regime,
the localization of the maximum 2PE intensity was found to shift closer to the surface<sup>1</sup> and the 2PE imaging
depth limit appears strongly limited by near surface fluorescence.<sup>2</sup> In this work we computed the illumination
and the photobleaching distribution<sup>3</sup> in order to characterize the effects induced by scattering. The simulations
have been performed for different scattering coefficients and different focus depth. An experimental test has
been carried out by imaging, with 0.9 numerical aperture objective, thick scattering fluorescent immobile sample
(polyelectrolyte gel). Results confirm that under these conditions no photobleaching effects due to scattering
occur close to the surface.