Binary Phase Gratings for Materials Processing

The feasibility of using a diffractive optical element, a phase grating, as a beam handling device for use in industrial laser material processing is examined. The binary phase grating is an efficient beam splitting device and is useful in many materials processing operations (welding, cutting, soldering, drilling) where a high degree of parallelism could significantly improve process throughput. Overall efficiency of etched quartz binary gratings agrees well with published predictions (nominal 70–90%). Copies of the grating formed in PMMA (acrylic) survived preliminary life tests (more than 1000 9-J pulses from a commercial multimode Nd-Glass laser) with no measurable change in performance. Conventional Small Outline (SO) IC electronic packages were both laser soldered and welded to substrates with one laser pulse. Beam splitting uniformity of desired images is within 10% for the original quartz gratings and for some PMMA copies. Conventional doublet achromat and planoconvex lenses are adequate for maintaining 10% uniformity of intensity. Splitting uniformity is experimentally evaluated with energy and focused spot (burn) tests on kapton (polyimide) and thin and thick metal samples using a pulsed industrial Nd laser.