  Pushing the limits of precision and reproducibility in ultrafast laser-based
nanostructuring requires detailed control over the properties of the
illumination. Most traditional methods of laser-based manufacturing rely on the
simplicity of Gaussian beams for their well-understood propagation behavior and
ease of generation. However, a variety of benefits can be obtained by moving
beyond Gaussian beams to single or multiple tailored beams working toward
optimal spatial and temporal control over the beam profiles. In this chapter,
we center our attention on methods to generate and manipulate complex light
beams and the resulting material interactions that occur in response to
irradiations with these non-traditional sources. We begin with a discussion on
the main differences between Gaussian and more complex light profiles,
describing the mechanisms of phase and spatial control before narrowing the
discussion to approaches for spatial structuring associated with materials
processing with ultrashort laser pulses. Such structuring can occur in both
far-field propagating architectures, considering rapidly varying spatial
profiles generated mechanically or optically, as well as near-field,
non-propagating beams associated with plasmonic and dielectric systems. This
chapter emphasizes some of the unique abilities of complex light to shape
materials at the nanoscale from a fundamental perspective while referencing
potential applications of such methods.
