Using Molecular Marking in Security Holograms

Subject of study. The capabilities of the technologies for marking products and security holograms based on the analysis of the spectral properties of molecular structures introduced to the holograms are considered in combination with the adoption of quantum dots and magnetic microparticles (MPs). The primary focus is on the issues of the analysis of the Raman spectra of molecules excited by plasmonic-resonant electromagnetic fields. Method. Modern technologies for hologram security are based on the use of various protective optical effects concealed from visual observation. These effects reveal themselves only under the relevant illumination of holograms when specialized optical equipment is employed. Unique methods for marking and identification of holograms using the magneto-optical, fluorescent, and spectral properties of the emission of MPs and molecular structures with sizes ranging from tens of nanometers to tens of micrometers, which are excited by localized electromagnetic fields, are considered. The plasmonic-resonant methods for the excitation of marking molecular labels introduced into the hologram structures are the most relevant, together with the arising spectra of surface-enhanced Raman scattering that are used for the identification and authenticity verification of the holograms. Main results. The use of plasmonic-resonant methods for concentrating electromagnetic fields for the excitation of marking molecular labels was demonstrated to be able to ensure the amplification of their Raman emission by several orders of magnitude, which results in the significant enhancement of recognizability and identification of security holograms. Practical significance. The technologies for hologram protection proposed in this work are based on the combination of different types of markings such as hidden holographic images, magneto-optical and fluorescent images of MPs, and Raman spectra of molecular structures that are enhanced by plasmonic-resonant methods. These technologies significantly increase the reliability, security, and authenticity of the marking and its identification. The results of this study will help in forming the basic technical requirements for design of portable devices for the identification of security hologram markings. (C) 2022 Optica Publishing Group