Planar optics constructed from subwavelength artificial atoms have been suggested as a route to the physical realization of steganography with controlled intrinsic redundancy at single-pixel levels. Unfortunately, two-dimensional geometries with uniform flat profiles offer limited structural redundancy and make it difficult to create advanced crypto-information in multiplexed physical divisions. Here, we reveal that splashing three-dimensional (3D) plasmonic nanovolcanoes could allow for a steganographic strategy in angular anisotropy, with high resolution, full coloration, and transient control of structural profiles. Highly reproducible 3D morphologies of volcanic nanosplashes are demonstrated by creating a standardized recipe of laser parameters. Such single nanovolcanoes can be well controlled individually at different splashing stages and thus provide a lithography-free fashion to access various spectral responses of angularly coordinated transverse and vertical modes, leading to the full-range coloration. This chip-scale demonstration of steganographic color images in angular anisotropy unfolds a long-ignored scheme for structured metasurfaces and thereby provides a paradigm for information security and anticounterfeiting.
Keywords: angular anisotropy; laser splashing; plasmonic nanostructures; steganography; structural color.