Lead crystal is traditionally engraved by cutting grinding and sandblasting with the drawbacks of: a large effort of manual labour; difficulty of realising small detail in writing and fine line drawing; environmental impact by residues from grinding polishing etching; tendency of engraved and sandblasted surfaces to get dirty from dust and fingerprints. The Fraunhofer IWS Dresden developed the laser technique of subsurface engraving of lead crystal. Depths up to several centimeters are covered in this way. This gives rise to a novel manner of glass decoration: Without affecting the polished surface two- and three-dimensional images can be created inside a lead glass block. Within a normally transparent material the high intensity in the focus of a laser beam gives rise to non-linear absorption phenomena. As a result microscopic cracks are generated on a narrowly localized spot which makes the spot look white by multiple light reflection. The images are created dot by dot with the workpiece being moved in two or three dimensions. The controlled motion is based on real-time position data acquisition and processing. In this way repetition rates up to 500 Hz are reached.
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