  The influence of a deformable mirror on spatial light modulation in ultrafast
lasers processing is demonstrated. The deformable mirror was integrated into an
optical setup which contains an additional lens for generating a nearly linear
focus shift in the focal plane behind the f-theta lens. The deformation of the
mirror surface can be described by the Zernike terms Defocus, Astigmatism, and
a combination of both, resulting in a cylindric lens behavior. The influence of
the mirror surface deformation in this optical setup on the intensity
distribution in the focal plane was simulated. From the simulation results, the
caustic in the focal plane was calculated. The simulation results were compared
to experiments using a picosecond laser with a maximum pulse energy of about 60
$\mu$J. We demonstrate that the initial astigmatism of the raw beam can be
reduced using the deformable mirror. High linearity in the focus shift ($R^2
>98$%) and the generation of elliptical/ line intensity distributions are
shown. Line intensity distribution was used to demonstrate slit drilling
application in thin metal foils.
