Large aperture continuous phase diffractive optical element to realize uniform focal spot

Uniform focal spot, with flat top, steep edge, low side lobe and high light efficiency, is required in many high power laser system. Using diffractive optical element (DOE) to realize such uniform illumination has many advant ages, such as high light efficiency of pure phase modulation, strong flexib ility of phase design and so on. A kind of hybrid algorithm based on hill-c limbing and simulated annealing is utilized for phase design, owing to the strong convergence of the hill-climbing and the global optimization potenti al of the simulated annealing. A continuous phase DOE with diameter 100 mm has been fabricated by a rotating hollowed-out mask and ion-etching on the K9-glass substrate. The interferogram of the DOE is given to show the smoot hness of the phase distribution. The intensity distribution of the focal sp ot are measured by a general CCD, acid a series of attenuators are used to increase the dynamic range of the measurement. The results after data-proce ssing show that the uniform focal spot with certain uniformity at the main lobe, sharp edge, low side lobe and without sharp peak at the zero order ha s been obtained. (C) 2001 Elsevier Science Ltd. All rights reserved.