Arrangement and method for checking optical diffraction structures on documents

US7345747B2 · kind B2 · utility

Assignee

• Cross Match Technologies, Inc. · US

Inventors

• Juergen Hillmann · Jena, DE
• Thomas Burkhart · Dahn, DE
• Kevin Koelling · Weimar, DE

Key dates

• Filing date: Apr 14, 2005
• Grant date: Mar 18, 2008
• Expiry date: Mar 17, 2026

Classification

• Technology area (CPC G): Physics
• CPC primary: G03H2222/34
• WIPO field: Optics
• WIPO sector: Instruments

Abstract

The invention is directed to an arrangement and a method for checking optical diffraction structures (e.g., kinegrams) on documents. The object of the invention, to find a novel possibility for checking optical diffraction structures on documents which permits detection of the presence and authenticity of optical diffraction structures quickly and economically with respect to apparatus, is met according to the invention in that the sensor unit is arranged orthogonally above the support surface of the document, and in that the illumination unit contains at least two monochromatic light sources which are arranged so as to emit light bundles at defined incident angles with respect to a surface normal of the document directed to the diffraction structure and which can be switched on sequentially. At least one light source has an incident angle that corresponds in direction and degree to a diffraction angle at which an intensity maximum of the diffraction pattern that is generated in a structure-specific manner would occur if the diffraction structure were illuminated from the direction of the sensor unit.