Set of line gratings as a diffraction structure protecting optical signs against copying: new proposal including colorimetric aspects

Well known properties of diffraction gratings are connected with their response to wavelength and polarization state of light incident on a grating. Although diffraction gratings are used as one of structures in modern optical security sings, their interesting properties seem to be rather rarely taken into consideration for distinguishing between originals and 'illegal' copies of optical marks. In this paper a relative simple diffraction structure and corresponding alterative method of inspection are proposed. This method can be particularly useful for machine reading, although its usability for visual inspection can also be considered.