Diffractive beamshaping elements at the fabrication limit

We treat the generation of flat-top intensity distributions, as required for laser applications at short wavelengths. To obtain high fill factors and almost arbitrary shapes, arrays of diffractive Fresnel zone plates at the fabrication limit are investigated. The angular power spectrum noise due to the binarization of the transmission phase function is smoothed using an incoherent source. The remaining zeroth order is ommited by the addition of a constant offset phase to the transmission phase function of the array. An analysis of etch-depth errors as well as an investigation of multilevel elements is appended. Simulation results, obtained by a 2-D analysis for radial symmetry, are compared to measurements.