Unclonable Three-Level Holograms for Two-Factor Visual Authentication via One-Step Cascade-Nanostructure Imprinting

Digital authentication technologies are increasingly threatened by the rapid advance of artificial intelligence and sophisticated cyberattacks. Against this backdrop, analog approaches that enable intuitive visual inspection and are physically unclonable are gaining prominence. This work develops a low-cost route to fabricate large-area hologram films with cascade nanostructures, establishing a robust two-factor authentication platform. Three-level silicon master molds are produced in a single dry-etching step, and the hologram films are replicated via nanoimprint lithography. By integrating a computer-generated holography design, the holograms selectively suppress the conjugate image, enabling instant visual authentication using a portable flashlight. To strengthen security, each film incorporates fiducial marks that designate the inspection site for a portable microscope. The local nanopattern can be converted into a security code for secondary verification. Consequently, the proposed cascade-hologram strategy combines cost-effectiveness, high fidelity, and durability with enhanced anticounterfeiting performance, supporting deployment across products, including electronic devices, apparel, and consumer goods.