Direct laser writing structural color for reversible encryption and decryption in different mediums

Structural color (SC) has enormous potential for improving the visualization and identification of functional micro/nano structures for information encryption and intelligent sens-ing. Nevertheless, achieving the direct writing of SCs at the micro/nano scale and the change of color in response to exter-nal stimuli simultaneously is rather challenging. To this end, we directly printed woodpile structures (WSs) utilizing fem-tosecond laser two-photon polymerization (fs-TPP), which demonstrated obvious SCs under an optical microscope. After that, we achieved the change of SCs by transferring WSs between different mediums. Furthermore, the influence of laser power, structural parameters, and mediums on the SCs was systematically investigated, and the mechanism of SCs using the finite-difference time-domain (FDTD) method was further explored. Finally, we realized the reversible encryption and decryption of certain information. This find-ing holds broad application prospects in smart sensing, anti-counterfeiting tags, and advanced photonic devices. (c) 2023 Optica Publishing Group