Embossed diffractive optically variable devices are becoming increasingly familiar security items on plastic cards, banknotes, security documents and on branded goods and media to protect against counterfeit, protect copyright and to evidence tamper. Equally as this devices become both more widely available there is a pressing requirement for security technology upgrades to keep ahead of technology advances available to potential counterfeiters. This paper describes a new generation electron beam DOVID origination technology particularly suitable for high security applications. Covert marking of security devices is provided using the DNA matrix by creating and verifying unique DNA sequences. This integration of this into practical security features in combination with covert features based on DNA matrix authentication and other more straightforwardly authenticable features to provide multi- technology security solutions will be described.
This contribution concentrates on theoretical studies of diffraction processes in surface-relief gratings. The characterization of diffraction processes and mechanisms is presented and discussed, together with the regions with typical diffraction regimes. The attention is also devoted to phase synchronism: angular and volume types of synchronisms are distinguished. Some typical examples of modeling are considered for a class of binary surface-relief gratings. Rigorous coupled-wave analysis is used for modeling, and some interesting result of volume phase synchronism are presented and discussed. Finally, features of a fundamental resonator region, which is characterized by strong energy interchange processes, since a new diffraction order starts to become real propagating, are described and interpreted.
This paper concentrates on theoretical studies of diffraction process in periodic diffractive structures-- gratings. Its contribution can be seen on several levels: it reviews the terminology and different approaches of diffraction methods, presents a new form of diffraction process characterization (described by the diffraction efficiency), and discusses five regions with typical diffraction regimes. In more detail, this contribution analyses the mechanisms during the diffraction process in terms of phase synchronisms, and distinguishes between angular, transversal and Bragg (volume) phase synchronisms. Using such terminology, diffraction regions are discussed in more detail. The case of Bragg diffraction is treated by both an approximate (Kogelnik's method) and a rigorous method (rigorous coupled-wave analysis-RCWA), and these two methods are compared. Properties of high-spatial frequency gratings are summarized, and resonant regions, characterized by strong resonant processes, are introduced. Finally, three different methods for the analysis of diffraction gratings are reviewed: RCWA, Kogelnik's approximate method, and approximate methods of transmittance function. The review of basic transmittance methods is made (primitive, modified), and a different approach (TCWA-transmittance coupled-wave analysis) is presented.