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In today's world, the fight against counterfeiting is more critical than ever. Counterfeiting affects about 3% of global trade, posing significant risks to the economy and public safety. From fake pharmaceuticals to counterfeit currency, the need for secure and reliable authentication methods is paramount. Authentication labels are commonly used – such as holograms on bank notes and passports – but there is always a need for new unfalsifiable technologies.
This is where new groundbreaking research recently published in Applied Sciences comes into play. Led by a team of scientists from Oxford University, the University of Southampton, and Diamond Light Source, the UK’s national synchrotron, the work focuses on developing a new technology for writing and reading covert information on authentication labels. This technology leverages the unique properties of Ge2Sb2Te5 thin films, which can change their structure when exposed to specific types of laser light. By using circularly or linearly polarised laser light, the researchers can encode hidden information in these thin films. This information can then be revealed using a simple reading device, making the technology both advanced and accessible. The paper is called 'Application of Photo-Induced Chirality in Covert Authentication' and explains how photo-induced chirality in Ge2Sb2Te5 thin films can be exploited to improve authentication.
The significance of this research lies in its potential applications. Authentication labels are essential in various industries, including pharmaceuticals, electronics, and currency. The ability to encode and read covert information securely can help prevent counterfeiting and ensure the authenticity of products. Moreover, the technology's reliance on existing manufacturing methods makes it a practical solution for widespread use.
To create these new authentication labels, the authors deposited 55nm thick film on a disk substrate. After that, author, Dr Konstantin Borisenko, Research Computing Administrator at University of Oxford explained,
We ‘wrote’ a predesigned pattern of spots using a laser and a polariser. Then we used the B23 beamline at Diamond Light Source to ‘read’ the film using circular dichroism (CD), a type of spectroscopy, and recorded the CD spectra in transmission mode.
The spectra were acquired using a highly collimated and focused synchrotron beam of about 100 µm in diameter in a 200 nm to 600 nm wavelength range with 5 nm intervals (Fig. 1).
The spectra showed that the highest magnitude was observed at 520 nm. The authors then compared the signal obtained from reading the CD intensity at 520nm on the B23 beamline, and on a standalone label reader, using a green LED as a light source (Fig. 2).
The results showed that the polarisation of a laser beam can be successfully recorded on an authentication label. Dr Rohanah Hussain, Senior Beamline Scientist at Diamond explained,
This information was read using the synchrotron radiation circular dichroism (SRCD) imaging at Diamond B23 that validated a simple, standalone, in-house built instrument which gave very similar results and could be used as an affordable reading device.
The prepared label showed no deterioration in signal when retested after being stored under ambient conditions for at least six months. Preliminary experiments also indicated that the label and the polarisation signal remained stable even after short heat treatment at 100°C, suggesting longer-term stability.
Dr Borisenko concluded,
We have demonstrated a new technology for writing a covert code invisible to the naked eye. This code can only be revealed if the direction of rotation of the polarisation of light encoded in the label during laser writing is measured by a suitable reading device. A prototype of the simple reading device is outlined, which qualitatively provides the same reading outcome as more sophisticated approaches using circular dichroism spectroscopy and imaging. The observed strong signal from the reading device supports further miniaturisation of the labels. This feature may enable this approach to be integrated with the technology used in existing holographic security labels to increase the level of security.
For more information on the B23 beamline, and Synchrotron Radiation Circular Dichroism (SRCD) please contact Principal Beamline Scientist Giuliano Siligardi: [email protected]
Application of Photo-Induced Chirality in Covert Authentication - Appl. Sci. 2024, 14(21), 9743; https://doi.org/10.3390/app14219743 Published: 24 October 2024
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