Abstract
A customized UV nanosecond pulsed laser system has been developed for the fast generation of tamper-proof security markings on the surface of metals, such as stainless steel, nickel, brass, and nickel-chromium (Inconel) alloys. The markings in the form of reflective phase holographic structures are generated using a laser microsculpting process that involves laser-induced local melting and vaporization of the metal surface. The holographic structures are formed from an array of optically-smooth craters whose depth can be controlled with ± 25nm accuracy. In contrast to conventional security markings, e.g., engraved serial numbers, etched part numbers and embossed polymer holographic stickers, which are only attached to the metal products as an adhesive tape, the phase holographic structures are robust to local damage (e.g. scratches) and resistant to tampering because they are generated directly on the metal surface. This paper describes a novel laser-based process for security marking of high-value metal goods, investigates the optical performance of the holographic structures, and demonstrates their application to watches.
Highlights
Trade of counterfeit goods causes serious harm to the global economy and society, affecting both customers and companies [1]
This paper describes a novel laser-based process for security marking of highvalue metal goods, investigates the optical performance of the holographic structures, and demonstrates their application to watches
The data underlying this work are commercially confidential
Summary
Trade of counterfeit goods causes serious harm to the global economy and society, affecting both customers and companies [1]. 2.2 Optical setup for reading the holograms the holographic structures may be read using a low-cost handheld laser pointer, in order to properly evaluate their optical performance the optical setup shown in Fig. 1 was employed In this setup, a He-Ne laser beam (λ = 632.8nm) was expanded to a 1.8mm diameter spot (measured at 1/e2 of its maximum intensity) using a beam expander (BEX) that consisted of two (plano-concave and plano-convex) lenses of focal lengths -30mm and 75mm. 3.2 Results Due to the intended application of the holographic structures for anti-counterfeiting security marking, the pulse energies used for the generation of optically-smooth deformations on the surface of the studied metals cannot be provided in detail. Since the Inconel® alloys contain a small amount of sulphur (< 0.015%) and were processed in air, it seems likely that the dΥ/dT value could change sign at some pulse energy (temperature), thereby leading to a complex flow of the melt and the formation of protrusions in the centre and around the edge of the melt pool
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
