Superimposed CGHs on metals using laser ablation of diffractive pixels A special interference process allows the fabrication of computer-generated holography (CGH) as carrier of information which can’t be recognized with the human eye. The CGHs consist of N * M pixels which, when illuminated with coherent light, generate an imagine with the same pixel dimensions in a Fourier plane. Several CGHs can be written on the same area. When illuminated with the same coherent reading beam, they appear separately in different directions (diffraction orders).