A new printing method lets us make images smaller than we've ever before managed — much smaller than the width of the average human hair. What's more, these images are in colour.
Invented by scientists at the Technical University of Denmark, the new technique relies on a surface covered with tiny metal plates only a few micrometres wide. A high-intensity laser hits the plates for a precise, but tiny, amount of time. These fast short bursts keep the heat from spreading from one part of a plate to another, but is also sufficient to melt the metal until it has a specific texture.
Each texture produces a colour through special kinds of waves called surface plasmons. Metal surfaces have a bunch of free electrons swimming around on top of them. They are not attached to any specific atom — that's why electrons are such good conductors of electricity. When light excites them, they start to move. In this case, they oscillate across the surface as plasmon waves. These plasmons also give off light, although it's rarely light that can be seen by the naked eye.
The textured metal surface serves as an amplifier, giving the coloured light emitted by the plasmons a boost. In the past, plasmons have been used to create holograms that don't change colour even if you change the angle of observation. In this case, plasmons are creating still images, smaller than anyone has managed to make before.
[Source: Plasmonic colour laser printing]