Non-scanning 2-D laser cutting with computer-generated hologram and superposition of orthogonal polarizations for improving discontinuous image pattern

Abstract

Lasers are used in precise material processing because they can be focused into small region to achieve high energy densities. The conventional laser processing method has a limitation on the processing speed because it is performed by scanning a single spot. In order to overcome this problem, it is necessary to use a hologram to spatially distribute a high power or high energy laser beam on the target and simultaneously process it. In this dissertation, we propose a non-scanning 2-D laser cutting method using a phase-only computer-generated Fourier hologram. In general, a line image reconstructed by a phase-only Fourier hologram has a spatially fluctuating phase, so that a discontinuous pattern occurs due to interference between spots. This is the main reason for the difficulty of laser cutting using a hologram. In order to minimize this and to obtain continuous line images, the line target is divided into two targets and then reconstructed with orthogonally polarized beams, and they were crossed and superposed. Using computer-generated holograms which are designed and fabricated using this method, 2-D laser cutting was performed on polyimide film with a high energy laser without scanning process. The diffusion of the heat absorbed in the material was then calculated by the finite element method and compared with the experimental results.