<title>Design and manufacture of continuous-phase diffractive optical elements for beam transforms</title>

Abstract

In high power laser system, such as inertial confinement fusion and laser forming, the requirement for the intensity distribution of the focused laser profile must be top head, steep edge, low side lobe and concentrated high power performance in the main lobe. Diffractive Optical Element (DOE) is used to produce an arbitrary radiation distribution on the focal plane. It has the features of high diffraction efficiency, steep edge, small side lobes and high flexibility. A kind of hybrid algorithm based on hill- climbing and simulated annealing is utilized for phase design because of the ability of strong convergence of the hill-climbing and the global optimization potential of the simulated annealing. Continuous phase should be adopted to increase the light efficiency and decrease wide-angle scattering. The continuous phase DOE with diameter 100 mm has been obtained by gray-level mask and ion-etching on the K9-glass substrate. The DOE's interferogram is given to detect the precision of manufacturing. The manufacturing error, including depth error and alignment error, are analyzed. The intensity distribution of the focal spot is measured by a general CCD, and a series of attenuators are used to increase the dynamic range of the CCD. The results after data-processing show that the uniform illumination has been obtained.