Generation of pseudo-nondiffracting beams with use of diffractive phase elements designed by the conjugate-gradient method

Abstract

The design of diffractive phase elements (DPE’s) for generating pseudo-nondiffracting beams (PNDB’s) is carried out by employing the conjugate-gradient method. By selecting a trapezoid profile as the preset axial intensity distribution to guide the design and by using an error function with a weighting factor to evaluate the performance of the DPE, we develop a model design and obtain a satisfactory diffractive pattern of a single-segment PNDB. We demonstrate the effectiveness of the conjugate-gradient method in the design of DPE’s that produce multiple-segment PNDB’s in which two consecutive segments are separated by a dark region along the optical axis. We also evaluate the degree of nonuniformity of the axial intensity over a given axial region. The design results match the requirements quite well.