Securing valuable documents using computer generated holograms printed with photochromic inks (Secret-CGH)

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There is a substantial amount of counterfeit and therefore low-quality items in many contemporary industrial commodity items. This situation imposes serious problems of financial loss and/or safety and reliability issues to the general public. As a result, there is an ever-increasing need for the creation of innovative anti-counterfeiting techniques that are difficult to replicate and simple to detect. Various counterfeiting methods have been reported including ink, paper and digital technologies. Holographic labeling, radio frequency ID, and rapid responsive encodes are all examples of modern anti-counterfeiting technologies. However, the preparation and identification required for these approaches need the use of high-tech and expensive equipment, which limit their applications. The goal of the proposed project is the development of a novel approach for the security authentication of valuable documents using computer generated holograms (CGHs) printed with office printers and invisible photochromic inks. This approach shall provide high-security level features with low cost, simple production, and authentication processes without the need for dedicated devices. Besides, it shall ensure such a difficult replication or counterfeiting that it can be considered as an excellent way to secure valuable documents. Within the approach to be realized here, a dual-mode security level shall be achieved using a fluorescent photochromism, characterized by a color change for the naked eye from colorless in dark or in day light to colored when exposed to UV light. An additional protection shall be realized by encoding the valuable information of a document as holographic features in a single CGH. The CGH is secured by modifying it with an encryption key that incorporates the ink’s properties which are adapted/adjusted by doping the synthesized photochromic pigment with metal nanoparticles. This introduces additional degrees of freedom for encoding the information, providing a high level of security. Authentication is performed by capturing an image under UV light illumination and then digitally reconstructing the CGH by knowing the encryption key and its design parameters. Such a combination is intended to increase the protection of documents against forgery and counterfeit. Thus, the method will pave the way for the development of an innovative anti-counterfeiting technique enabling a difficult, near impossible replication of the CGHs in combination with a simple readout process.