Plasmonics And NanoTech Could Revolutionize The Science of Laser Printing

Plasmonics (Study of the interaction between electromagnetic field and free electrons in a metal) has been instrumental in devising new optoelectronic technologies and has immensely improved the performance of photovoltaic cells and LEDs over the past few years. Now, researchers at the Technical University of Denmark (DTU), have applied the principles of Plasmonics and nanotechnology in a way which could significantly upgrade the science of laser printing.

This allows one to print high resolution colour images with incredible precision, boasting of up to 120,000 dots per inch resolution, compared to a standard magazine's images which have only 300 DPI. To demonstrate the future printer’s staggering ability, DTU researchers have reproduced an image of the Mona Lisa in a space smaller than the footprint taken up by a single pixel on an iPhone retina display.

As published in the Nature Nanotechnology journal, this printer uses a special nanoscale-structure rather than dyes. Instead of using techniques such as e-beam lithography (EBL) or focused ion beam (FIB), which cannot be scaled to pre-design and print the plasmonic nanostructures, DTU researches have chosen a different method known as Laser post writing.

The nanoscale-structure is made up of rows and columns, each having a dimension of 100 nanometers. The structure is then covered by 20 nanometers of aluminium. At this point, the laser post-writing is introduced.When a laser pulse in incident on each nanocolumn, it melts and deforms. The temperature can be increased to up to 1500 degree centigrade for a few seconds. The intensity of the laser beam determines the extent of deformation, which consequently determines the colour that is reflected. A Low intensity laser beam produces small deformations of the nanocolumns resulting in a blue-purple toned picture. As our eyes can see only the reflected colours, in a similar way, a high intensity laser beam produces an orange-red coloured picture.

According to Professor N. Asger Mortensen from DTU Fotonik, small variations in the nanocolumns' geometry can change the wavelength of light that is absorbed, thus giving a different coloured appearance.

Professor Anders Kristensen from DTU Nanotech explained that the new printing technology can save data that is invisible to the naked eye including serial numbers or bar codes of products. The technology can also be used efficiently against fraud and forgery, as the products will be labelled in way that will make them impossible to reproduce and therefore make it easy to identify the fake from the original.

This technology is still at its infancy and needs to be significantly upgraded in order to be accessible for public use. However, it has already been patented and the research team is now concentrating on developing the technology further, so that it can replace the old printers.

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