Oct 13 2010
Sub-surface laser engraving has been used for many years to burn images, patterns or words inside solid materials, typically glass. When a computer system is used to drive the movements of the laser head, the engraving process itself becomes extremely precise and fast. And because the process does not disturb the surface of the material, the images, patterns or words inside the material will never fade or deteriorate.
For a long time, sub-surface laser engraving has been used exclusively for producing markings inside transparent materials. Zhongli Li at A*STAR’s Singapore Institute of Manufacturing Technology and co-workers1 have now demonstrated the possibility of laser engraving inside metals. Using a ‘Nd-YAG’ laser, the team was able to create a series of small holes, or microcavities, below the surface of a block of stainless steel (Fig. 1). After surface polishing, the laser markings become completely invisible.
The new technology is useful for fabricating hidden markings that are difficult to remove and could therefore be used to make security watermarks in the automotive, aerospace and military industries. The markings themselves can be revealed using non-destructive techniques such as X-ray imaging.
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