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To make effective and controllable diffractive gratings the optical system was developed combining high power laser source and interferometric dot-matrix approach. The paper presents considerations and some experimental data. The direct interference gratings were formed on flat metal surfaces like Ni, Cr, brass and stainless steel like AISI 305. Stable structures with adequate diffraction efficiency were obtained. The experimental setup used 1064 nm high-frequency pulsed fiber laser. The samples shows a threshold character of the interaction that requires beam-shaping devices to convert Gaussian distribution to flattop with minimum power losses. The resulting diffraction gratings had 275 lines per mm and nearly sine profile. Pi-shaper 6_6_1064 allowed most effective filling of metal surface thus giving good grating spatial uniformity and diffraction efficiency. Direct holographic gratings on flat metal surfaces were obtained and prototype dot matrix machine suggested. Spatial frequency needs to be increased to get better color separation and the range of materials expanded. We expect the new approach to improve quality and security features of holographic security marking. |
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