MATERIALS PROCESSING: Reflective optics minimize 'focus shift' in high-power materials processing

摘要

One of the challenges in any materials-processing application that uses high-power, high-brightness lasers (kilowatt power levels) is "focus shift"--the shift in focus position of a laser beam at the workpiece due to thermal lensing effects caused by nonuniform heating of the beam-delivery optics and coatings, among other factors. Not only does focus shift change the beam diameter at the workpiece, but it also causes changes in the relative angle of the focused beam as well as the beam's power distribution, making it more Gaussian than the typical top-hat profile. But by studying the properties of optical materials and the various methods for laser-beam delivery, scientists at Trumpf (Ditzingen, Germany and Plymouth, MI) have developed an optimized beam-delivery system that makes use of reflective optics to minimize focus shift.