| 摘要 |
<p>An optically variable surface pattern (1) includes at least one representation of graphic configuration. Surface portions (3, 4, 5) of a predetermined kind are associated with each representation. Upon being illuminated with visible light the representations are visible in the form of images comprising comparatively light and dark points at different viewing directions. The surface portions (3, 4) associated with light points of at least one of the representations, have grating structures with a number of lines of less than 250 lines per millimetre so that many diffraction orders occur in the visible range. The profile shapes of the grating structures are so selected that a maximum possible proportion of the diffracted light is diffracted into higher diffraction orders. That provides that the corresponding representation appears achromatically. So that in addition the ratio between the light which is diffracted into positive diffraction orders and the light which is diffracted into negative diffraction orders is as great as possible, grating structures with an asymmetrical profile shape and in particular a sawtooth profile shape are to be used.</p> |
