Colouration by surface nanostructuring has attracted a great deal of
attention by the virtue of making use of environment-friendly recyclable
materials and generating non-bleaching colours [1-8]. Recently, it was found
possible to delegate the task of colour printing to laser post-processing that
modifies carefully designed and fabricated nanostructures [9,10]. Here we take
the next crucial step in the development of structural colour printing by
dispensing with preformed nanostructures and using instead near-percolation
metal films atop dielectric-metal sandwiches, i.e., near-percolation plasmonic
reflector arrays. Scanning rapidly (~ 20 {\mu}m/s) across 4-nm-thin island-like
gold films supported by 30-nm-thin silica layers atop 100-nm-thick gold layers
with a strongly focused Ti-sapphire laser beam, while adjusting the average
laser power from 1 to 10 mW, we produce bright colours varying from green to
red by laser-heating-induced merging and reshaping of gold islands. Selection
of strongly heated islands and their reshaping, both originating from the
excitation of plasmonic resonances, are strongly influenced by the polarization
direction of laser illumination, so that the colours produced are well
pronounced only when viewed with the same polarization. Conversely, the laser
colour writing with circular polarizations results in bright
polarization-independent colour images. The fabrication procedure for
near-percolation reflector arrays is exceedingly simple and scalable to mass
production, while the laser-induced modification occurs inherently with the
subwavelength resolution. This unique combination of remarkable features makes
the approach developed for laser colour writing readily amenable for practical
implementation and use in diverse applications ranging from nanoscale
patterning for security marking to large-scale colour printing for decoration.Comment: 29 pages, 17 figure
