Usual laser printers have some 600 dots per inch (dpi) resolution (that is fine, our eyes wouldn't be able to appreciate resolution over 300dpi). Some of the very best can reach 2,400dpi.
Now researchers at the Technical University of Denmark have pushed resolution to a whole new dimension: 127,000 dpi! At this kind of resolution one could print a photo of the Mona Lisa by Leonardo in the space smaller than a single pixel of an iPhone retina display.
They have achieved this amazing result by using plasmonic metasurfaces coated with a 20nm layer of alumina. A laser heats up the surface of the dot to 1,500°C for a few nanoseconds, long enough to melt the alumina surface and create a dent. The strength of the pulse determine the depth of the dent, which in turns creates a colour... Low intensity laser pulses lead to smaller deformation of the alumina surface resulting in blue-purple hues, stronger intensity creates larger deformation that results in orange and yellow reflection.
Clearly this high resolution can be used for high density storage of information and to create labels that are more difficult to forge.