Multiplexed surface reliefs on azopolymer thin films

Multiplexing is a method in which multiple information is stored or combined in a common medium. In photolithographic applications, spatial and temporal multiplexing can be used to design complex structured surfaces as superposition of simple profiles on the surface of a photosensitive materials able to respond to a time-averaged light pattern. Azopolymers are promising material systems in that sense, as they can be directly photo-structured in a reversible way over large scales with high quality, by simply controlling the spatiotemporal distribution of light irradiated on their surface. Not involving the typical chemical development of standard photoresists, the direct light-induced surface topography of azopolymer can be further modified after structuration, resulting a suitable platform to encode multiplexed information in a topographic surface relief pattern. Here, we show a method that allows the fabrication of multiplexed azopolymer surface relief gratings through a computer controlled holographic illumination system. The ability of our setup in accurately and digitally manipulating the evolution of the geometry of a simple sinusoidal intensity pattern is here exploited for the realization of quasicrystalline surface relief gratings, that can be tuned to have both positive and negative topography while preserving the multiplexed grating-vector information encoded in their far-field light diffraction pattern. Our results pave the way toward the realization structured surfaces able to convert multiple information in a single complex topographic profile for application in optics and cryptography.