Method for checking authenticity of a hologram and a reading device for the performance of the method

A method for determining the authenticity of a hologram, characterised by the following steps:

• a) The hologram (1) to be checked is illuminated by a restoration ray (2);
• b) The diffraction ray (3) of the first order of the wave field created at the hologram is imaged on a first photo-sensitive element, in particular a CCD target (5);
• c) The diffraction ray (4) of the zeroth order of the wave field created at the hologram is imaged on a second photo-sensitive element, in particular a CCD target (6);
• d) The speckle intensity distributions of the diffraction rays of the first and second orders imaged on the photo-sensitive elements are determined for at least two phase relationships of the restoration ray and correlated with each other to obtain a correlation speckle intensity distribution for the relevant order of diffraction;
• e) The correlation speckle intensity distributions determined for the relevant orders of diffraction are correlated with each other, particularly subtracted from each other pixel by pixel.

A reading device for the checking of holograms

• characterised by
• an apparatus (30) to generate a restoration ray (2) to illuminate a hologram (1) to be checked;
• an imaging optical element (14, 8) to image the diffraction ray (3, 4) of the first and zeroth orders of the wave field created at the hologram (1) on first and second photo-sensitive elements, in particular CCD targets (5, 6);
• an apparatus (30) to generate first and second reference rays (7, 10) which can be brought to interference with the diffraction rays (3, 4) by means of an imaging optical element;
• means (32) to modify the phase relationship between the restoration ray (2) and the corresponding reference rays (7, 10);
• and
• means for the computer correlation of the interference pattern intensities determined at the photo-sensitive elements (5, 6).