Optical information carrier having diffractive features and diffraction

Abstract

An information carrier is in the form of a composite laminate with a first, a second and a third layer having refractive indices n3, n4, n5 respectively. The second layer forms structures by only partially covering the first layer. The third layer covers over the second layer or the first layer in direct contact therewith. The surface on the first layer has surface elements with first and second diffraction structures which produce a visually verifiable authenticity feature or which serve for reading out the information contained in the structures formed by the second layer. The refractive indices n4 and n5 are substantially real in the visible range and therefore the second and third layers are transparent. The differences .vertline.n4-n3.vertline. and .vertline.n5-n3.vertline. are greater than 0.2 over large parts of the visible range so that the first diffraction structures produce visible diffraction effects independently of the structures formed by the second layer. The differences n4-n3 and n5-n3 are of approximately equal magnitude in the visible range so that the structures formed by the second layer are invisible. In a second predetermined spectral range .LAMBDA., the absolute difference .vertline.n5-n4.vertline. is at least 0.1 so that in the reading operation using a suitable light beam the structures formed by the second layer produce a measurable change in the light beam which is diffracted at the second diffraction structure.