Reconfigurable Hologram Response to Liquid via the Femtosecond Laser Direct Writing of 3D Micropillars

Reconfigurable and tunable holograms hold significant practical value in the fields of anti-counterfeiting, optical security, and information display due to their ability to reprogram holographic patterns and create variable visual effects. However, current encryption techniques face challenges in achieving rapid encryption/decryption and ensuring consistent methods. In this study, a method for producing a reconfigurable encryption hologram utilizing the deformation and recovery properties of micropillars in response to liquid is demonstrated. Micron-scale micropillars are fabricated using femtosecond laser two-photon polymerization. By exploiting the rapid deformation and recovery capabilities of micropillars with specific pitches and aspect ratios in response to liquids, micropillar structures and holograms are combined to construct reconfigurable holograms. The encrypted pattern information in the reconfigurable holograms is only readable following immersion in alcohol and laser irradiation. The proposed method offers a facile, reversible, reusable, and practical solution for information encryption, with significant potential in anti-counterfeiting and optical security.