Design and analysis of diffractive optical elements for flattening of single modal Gaussian beams

A design method of diffractive optical element is presented for converting a single modal Gaussian beam into a flat-top beam in the far field of the source. The design is based on geometrical method and modified Gerchberg-Saxton method. Geometrical method derives from the conservation of energy and the constant optical path length. This method could supply initial phase distribution of the modified Gerchberg-Saxton method. To find the optimization design results, the modified Gerchberg-Saxton method is important to choose the feedback factor to increase the convergent speed. In addition, tolerances and limitations of such elements result in a reduction of the diffraction efficiency and as a result of stray light. Further study indicates that deviation of the laser wavelength, incident beam, and observation plane can greatly influence flat-top beam shaping quality. On the basis of theoretical and experimental results, limitations for the application of diffractive beam shaping elements are investigated.