Laser processing over a large area by wavefront-controlled scanning

In the processing of laser materials, the scanning area is limited by the extent to which the laser focus can be maintained within a plane. In order to increase the processing area, one has to enlarge the size of the laser focal spot, and, therefore, reduce the peak intensity and spatial resolution. In this paper, the authors report on a method that extends the processing area by controlling the wavefront of a laser beam using adaptive optics. By adding Zernike modes to the laser beam wavefront, the axial (along the beam propagation direction) location of the focal spot can be tuned within a range larger than the confocal length (two times the Rayleigh length), while the lateral spot size (and, thus, peak intensity and resolution) is maintained throughout the tuning range. A wave propagation model that simulates the propagation of a wavefront-controlled beam is used to compare with the experimental results, which are also confirmed by Zemax calculation. Laser trepanning of circular holes with consistent size on a wide polypropylene sheet is demonstrated. This work shows the potential of tailoring the phase of a laser beam for improving the accuracy and throughput in large-area laser processing of materials.