Tiny masterpiece

Researchers from DTU Nanotech and DTU Fotonik have reproduced a colour image of the Mona Lisa which is less than one pixel on an iPhone Retina display. The laser technology allows printing in a mind-blowing resolution of 127,000 DPI. In comparison, magazines are normally printed in a resolution equivalent to 300 DPI.

It is claimed this nanotechnology breakthrough will revolutionise laser printing technology, allowing the printing of high-resolution data and colour images of unprecedented quality and microscopic dimensions.

Printing the microscopic images requires a special nanoscale-structured surface. The structure consists of rows with small columns with a diameter of 100nm each. This structured surface is then covered by 20nm of aluminium. When a laser pulse is transmitted from nanocolumn to nanocolumn, the nanocolumn is heated locally, after which it melts and is deformed. The temperature can reach up to 1500°C, but only for a few nanoseconds, preventing the extreme heat from spreading.

The intensity of the laser beam determines which colours are printed on the surface, since the extent of column deformation decides which colour is reflected. Low-intensity laser pulses lead to a minor deformation of the nanocolumn, resulting in blue and purple colour tone reflections. Strong laser pulses create a drastic deformation, which gives the reflection from the nanocolumn an orange and yellow colour tone.

Professor N. Asger Mortensen from DTU Fotonik explained: "Every time you make a slight change to the column geometry, you change the way it absorbs light. The light which is not absorbed is the colour that our eyes see. If the column absorbs all the blue light, for example, the red light will remain, making the surface appear red."

The DTU researchers believe that there is considerable scope for the application of the new laser printing technology in the security sector.

Professor Anders Kristensen from DTU Nanotech elaborated: "It will be possible to save data invisible to the naked eye. This includes serial numbers or bar codes of products and other information. The technology can also be used to combat fraud and forgery, as the products will be labelled in way that makes them very difficult to reproduce. It will be easier to determine whether the product is an original or a copy."

The new laser printing technology can also be used on a larger scale to personify products such as mobile phones with unique decorations or names. Automotive companies producing parts, such as instrument panels and buttons, are already taking a keen interest in the technology as it can simplify production.

For now, the researchers are focusing on developing the technology, so that it can replace the conventional laser printers in offices and homes.