Direct laser-writing of optical micro-structures for robust traceability marking of metal components

This paper presents a laser-based process for the direct generation of security markings (in the form of reflective phase holograms) on the surface of metals. In order to achieve optically smooth holograms, we use a nanosecond pulsed laser operating at a 355 nm wavelength. This approach allows the metal surface to be structured, either by melting or the combination of melting and evaporation, with the required sub-micron depth control. The interaction between the UV 35 ns laser pulses and the surface of a 304-grade stainless steel, 99% pure nickel and two nickel-chromium Inconel® alloys is investigated in details and described in this paper.