Abstract
This paper focuses on the development of flat diffractive optical elements (DOEs) for protecting banknotes, documents, plastic cards, and securities against counterfeiting. A DOE is a flat diffractive element whose microrelief, when illuminated by white light, forms a visual image consisting of several symbols (digits or letters), which move across the optical element when tilted. The images formed by these elements are asymmetric with respect to the zero order. To form these images, the microrelief of a DOE must itself be asymmetric. The microrelief has a depth of ~ 0.3 microns and is shaped with an accuracy of ~ 10–15 nm using electron-beam lithography. The DOEs developed in this work are securely protected against counterfeiting and can be replicated hundreds of millions of times using standard equipment meant for the mass production of relief holograms.
Highlights
This paper focuses on the development of flat diffractive optical elements (DOEs) for protecting banknotes, documents, plastic cards, and securities against counterfeiting
The first flat optical elements were used to protect banknotes and plastic cards in the late 1980s. These optical security elements had the form of flat diffractive optical elements (DOEs) whose microreliefs, when illuminated by white light, formed images for visual control[1]
The authors of this study developed a method for synthesizing DOEs that create the effect of switching between two 2D images
Summary
This paper focuses on the development of flat diffractive optical elements (DOEs) for protecting banknotes, documents, plastic cards, and securities against counterfeiting. The first flat optical elements were used to protect banknotes and plastic cards in the late 1980s These optical security elements had the form of flat diffractive optical elements (DOEs) whose microreliefs, when illuminated by white light, formed images for visual control[1]. Over the past 30 years, the technology for the mass replication of optical security elements has experienced much development, allowing a single original security element to be replicated hundreds of millions of times, thereby substantially reducing the cost of these copies in large projects This is an outstanding achievement that has provided the technical conditions to be met by modern equipment to allow security elements to be replicated as numerous copies, with the microreliefs of the copied elements reproducing very precisely that of the original[3,4]. Everything is being counterfeited and forged: passports, ID cards, etc., and the same is true for optical elements
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