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

在许多当代工业商品中，存在着大量的假冒伪劣产品。这种情况给公众带来了严重的经济损失和/或安全和可靠性问题。因此，人们越来越需要创造出创新的防伪技术，这些技术很难复制，也很容易检测。据报道，各种造假方法包括墨水、纸张和数字技术。全息标签、射频ID和快速响应编码都是现代防伪技术的例子。然而，这些方法所需的准备和鉴定需要使用高科技和昂贵的设备，这限制了它们的应用。拟议项目的目标是开发一种新的方法，利用办公室打印机和隐形光致变色墨水打印的计算机生成全息图(CGH)对有价值的文件进行安全认证。该方法应以低成本、简单的生产和身份验证过程提供高安全级别的功能，而不需要专用设备。此外，它应确保如此困难的复制或假冒，使其可被视为保护有价值的文件的一种极好的方式。在这里要实现的方法中，应使用荧光光致变色实现双模式安全级别，其特征是肉眼的颜色从黑暗中的无色或白天的无色变为暴露在紫外光下的有色。通过在单个计算全息图中将文档的有价值的信息编码为全息特征来实现额外的保护。CGH通过使用包含墨水属性的加密密钥进行修改来确保安全，该墨水属性通过在合成的光致变色颜料中掺杂金属纳米颗粒来适应/调整。这为编码信息引入了额外的自由度，提供了高度的安全性。身份验证是通过在紫外光照射下捕获图像，然后通过知道加密密钥及其设计参数来数字重建计算全息来执行的。这样的组合旨在加强对文件的保护，防止伪造和伪造。因此，该方法将为开发一种创新的防伪技术铺平道路，该技术能够结合简单的读出过程实现困难的、几乎不可能复制CGH。

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.