Image multiplexing with laser-induced quasi-random plasmonic metasurfaces

Encoding several images in a single thin layer in such a way that they could be revealed independently by altering the conditions of observation of the layer has great potential for high-end anti-counterfeiting applications. Recently, the high contrast and dichroic properties of plasmonic colors have been soundly used to develop image multiplexing. Based on perfectly controlled anisotropic metallic nanostructures produced by e-beam lithography, the techniques developed so far have however some drawbacks. The images are too small to be observed by naked eye and the demultiplexing requires either monochromatic or polarized light.

Researchers at Laboratoire Hubert Curien and HID Global CID have developed a laser processing technique that allows printing large multiplexed images at low cost, with a high flexibility, and within very short times. The laser beam tunes the statistical properties of the nanoparticle assemblies, like their size-distribution, their shape anisotropy, and their average spatial distribution through self-organization mechanisms. Yet, the laser processing reproducibly controls the macroscopic optical properties of these random plasmonic metasurfaces and interestingly creates optical properties that are not accessible by other means. The team has demonstrated two- and three-image multiplexing under non-polarized white light, making the technology useful for real applications where an authentication is expected in few seconds.

Dalloz, N. et al. Anti-counterfeiting white light printed image multiplexing by fast nanosecond laser processing. Adv. Mater. 2021. https://doi.org/10.1002/adma.202104054

Destouches, N.et al., Laser‐Empowered Random Metasurfaces for White Light Printed Image Multiplexing. Adv. Funct. Mater. 2021, 2010430. https://doi.org/10.1002/adfm.202010430