Laser-driven plasmonic gratings for hiding multiple images†
Hiding several images in a single printing, which appear selectively at different angles of observation, is of great interest for applications in security, data storage or design. Here, we propose an easy-to-implement ink-free laser-based technique to print nanostructured patterns that encode different grey-level images revealed to the eye at specific observation angles. The angular selectivity is provided by diffraction gratings whose orientation can be continuously controlled at the micrometer scale through self-organization mechanisms triggered by laser light. A diffraction yield allowing easy observation with the naked eye is demonstrated, thanks to the use of a thin TiO2:Ag film that also prevents damage to the substrates. The technology based on laser scanning is demonstrated on transparent and flexible substrates that do not sustain high temperature. This ink-free marking technology is flexible, suited to large surfaces, rapid, and provides unique visual effects on any kind of transparent substrate.