FOCUS
WAVEFRONT control
WHAT DOES IT BRING TO LASER PROCESSING? The most direct benefit of spatial beam shaping is parallelization( see Figure 2 a-b). Instead of concentrating the available laser energy into a single Gaussian spot, the beam can be divided into multiple spots operating simultaneously. Early demonstrations already showed parallel surface structuring with several individually controlled spots, while more advanced holographic approaches have pushed this concept to arrays containing more than one thousand spots [ 4 ]. Such massive parallelization is particularly attractive with modern highaverage-power ultrafast lasers: increasing laser power can directly translate into increased throughput rather than excessive fluence on a single processing site.
Beam shaping can also modify the propagation properties of the processing beam. Non-diffracting beams, such as Bessel beams, maintain a narrow central intensity distribution over a much longer axial range than conventional Gaussian beams. This extended depth of focus is particularly advantageous for high-aspect-ratio drilling and cutting, where it reduces the need for precise axial positioning and enables rapid processing through thick transparent materials( see Figure 2 c). Their characteristic self-healing behavior also makes them less sensitive to partial obstruction and to perturbations induced by material modification or plasma formation during processing. In this case, beam shaping does not simply multiply the number of processing spots: it fundamentally changes how light energy is delivered inside the material.
At smaller scales, structured light provides additional degrees of freedom for surface functionalization. Femtosecond irradiation can generate laser-induced periodic surface structures( LIPSS) with periods down to the sub-wavelength scale. Since their orientation is strongly related to the local state of polarization, spatial polarization shaping enables different LIPSS orientations to be written simultaneously within the irradiated area. Vector beams with radial, azimuthal or more complex polarization distributions therefore open routes towards two-dimensional nanostructuring and
Figure 1. Principle of dynamic wavefront shaping. Typical dynamic modulators include( a) spatial light modulators( SLM),( b) deformable mirrors( DM) and( c) acousto-optic deflectors( AOD), each offering a different compromise between spatial resolution, speed and power handling.( d) An IFTA determines the phase modulation required to transform the incident beam into a target focal intensity distribution.
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