Diffractive optics as beam-shaping elements for plastics laser welding

This work reviews the use of diffractive optics for beam-shaping of high-power lasers $(50–100W)$ for welding and microwelding of plastics. While the use of lasers to weld plastics is well known, the use of diffractive optics to reshape lasers for welding of plastics has not been previously reported. By using inverse Fourier transformations diffractive lenses were designed and fabricated. An $80W$ fiber laser with a wavelength of $1084nm$ was coupled in air to the diffractive optical element (DOE) to shape the beam into predetermined patterns. These patterns were then reduced with standard optics to a desired size. Weld quality was assessed in terms of fidelity and replication of the original bitmap image that was used to design the DOE. Good results were obtained for both image fidelity and replication. In many cases the weld image retained the individual bitmap elements of the original artwork used to encode the DOE. It was also found that the overall efficiencies of the system were as high as 59% and weld times were less than $1s$. Weld joints were also determined to be relatively strong and weld circles as small as a few hundreds of $μm$ in diameter could be formed.