Reconfigurable holographic patterns for optical security multiplexing fabricated by 3D spatially modulated femtosecond pulses

Holographic patterns that integrate printings and holograms into a single device have received extensive attention in optical security owing to their attractive aesthetics and concealment. However, the sophisticated structures of metasurface-based optical devices require a time-consuming fabrication process, hindering the practical application of holographic patterns in optical security. In this study, a novel double-layer holographic pattern that employs simple microholes and microvoids as optical modulation units is designed and experimentally demonstrated. The two layers of the structure arrays are synchronously processed in a transparent material through a single serial-stitching of dynamic 3D spatially modulated femtosecond pulses that are proposed for the rapid fabrication of large-area multi-layered patterns. The fabricated holographic pattern appears as a dynamic grayscale image under white light incident at different angles and projects encoded holographic images under laser illumination. By transforming microholes into microcraters by ultrasonic treatment, the reconfiguration of the holographic pattern can be realized based on refractive index modulation using liquid immersion. The proposed reconfigurable holographic patterns with simple structures and visible sizes enable the recoding of multiple pieces of information, making them practical optical security elements with a wide range of applications in anti-counterfeiting and information encryption.