Scientists in the UK have used an ultraviolet nanosecond-pulsed laser to produce a tamper-proof hologram, which could replace serial numbers and barcodes and reduce the trade in counterfeit goods.
Manufacturers of high value goods like electronics and aviation parts etch serial numbers into products, use barcodes or place polymer holographic stickers on the items to provide identification and traceability of products and to assure customers of quality. However, serial numbers and barcodes are vulnerable to damage, and stickers are vulnerable to tampering and counterfeiting.
Scientists led by Professor Duncan Hand at Heriot-Watt University in Edinburgh are using an UV nanosecond-pulsed laser to sculpt unique holograms with micro-sized features directly onto the surface of metals, making them tamperproof.
Using the new method, individual laser pulses – at a rate of a few kilohertz – melt the metal surface in an extremely precise, localised way to produce optically-smooth impressions on the metal. By manipulating the laser beam to create specific patterns, holographic structures are produced that can act as security markings for high value products and components.
‘The holograms are visible to the naked eye and appear as smooth, shiny textures. They’re robust to local damage and readable by using a collimated beam from a low-cost, commercially-available laser pointer, so border agencies or consumers won’t need expensive technology to check an item’s authenticity. Actually, the holograms can also be read even using a flashlight from a smart phone,’ said Dr Krystian Wlodarczyk, a researcher working on the project.
The holograms can generate diffractive images containing alphanumeric characters or logos: the structure of the hologram is generated by either melting or a combination of melting and evaporation, with sub-micron depth control of the hologram individual features (called pixels).
The shape and geometry of the hologram pixels are very important because they affect the optical performance of the holographic structure. To obtain the maximum efficiency (contrast) of the diffractive image produced by the hologram, the pixels must have a certain depth and ideally a flat ‘optically-smooth’ base.
‘We’ve established that we can create the holograms on a variety of metals. We’re now investigating how to make them even smaller and more efficient and whether we can apply them to other materials. Recently, for instance, we have extended the process for use of such holograms on glass,’ Wlodarczyk added.
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