Counterfeiting of various documents, banknotes, or tickets is a common problem that can be encountered in everyday life, even when shopping. Recognizing the scale and seriousness of the problem, researchers at Kaunas University of Technology (KTU), Lithuania, decided to look for ways to further reduce the risk of counterfeiting by inventing a new method to produce holographic security labels.
Holograms have been used as an anti-counterfeiting tool for some time. Now, they can be seen on pharmaceutical packaging, brand labels, and even toys. Holograms are much more difficult for forgers to counterfeit than, for example, the watermarks on banknotes, as they require complex micro and nano technologies that traditional printing houses lack.
To enhance the level of holographic protection against forgery and to address this worldwide problem, Lithuanian researchers from KTU Institute of Materials Science came up with the idea of combining two technologically different methods.
One of them is a dot-matrix hologram made of small dots that refract light. "Each dot, which is barely smaller than a human hair, records a periodic structure made up of lines known as a diffraction grating. It causes the light to play in a way that is visible to the observer's eye, similar to a CD or DVD," explains one of the inventors, Dr. Tomas Tamulevičius.
Dr. Viktoras Grigaliūnas, a KTU researcher who also contributed to the development of the technology, adds that this dot-matrix hologram, although relatively faster and cheaper and used to expose large areas of the hologram, does not guarantee a very high level of protection.
This is why electron beam lithography is used to expose smaller areas of the hologram.
"It is a more advanced technology that allows to form high-resolution structures and is practically inaccessible to potential hologram counterfeiters," says Grigaliūnas, a researcher at the KTU Institute of Materials Science and head of the Research Laboratory of Nano and Microlithography Laboratory.
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