Development of large aperture diffractive optical element for beam smoothing

In this paper, the hybrid optimization algorithm, combing Hill-climbing and Simulated Annealing, is adopted to design the diffractive optical element (DOE) to realize beam smoothing. The performance of the DOE is improved by choosing suitable weight factor in the optimization, the non-uniformity is optimized to be less than 1% and the light efficiency greater than 95%. A large aperture DOE with diameter 180mm is fabricated by ion-etching with a hollowed-out mask. The intensity distribution of the focused spot is measured and a rather good intensity envelope has been obtained, without the center zeroth-order pulse but with a rather large high-frequency top modulation. Furthermore, to realize a true beam smoothing, improve the top uniformity and increase the tolerance of phase distortion, th