Influence of quantized diffractive phase element on the axial uniformity of pseudo-nondiffracting beams

The analysis of the diffractive phase elements (DPEs) that synthesizes pseudo-nondiffracting beams (PNDBs) in different axial regions are described. Those elements are designed by using conjugate-gradient method algorithm. To meet the requirement of lithography fabrication process, the obtained optimum continuous surface profile of DPEs must be quantized in the multilevel structure. In order to analyze the impact of different quantization levels, the axial-illuminance RMS variance of PNDBs for each quantized DPE is calculated and compared with each other. The compared results show that the axial illuminance of the PNDB of DPE with smaller-levels quantization fluctuates more rapidly than that of DPE with larger-levels quantization. Meanwhile, the analyses also show that the axial uniformity of the PNDB of DPE with a longer focal length is less sensitive to the quantization level.