GENERATION OF PSEUDO-NONDIFFRACTING BEAMS WITH USE OF DIFFRACTIVE PHASE ELEMENTS DESIGNED BY THE CONJUGATE-GRADIENT METHOD

The design of diffractive phase elements (DPE's) for generating pseudo -nondiffracting beams (PNDB's) is carried out by employing the conjuga te-gradient method. By selecting a trapezoid profile as the preset axi al intensity distribution ta guide the design and by using an error fu nction with a weighting factor to evaluate the performance of the DPE, we develop a model design and obtain a satisfactory diffractive patte rn of a single-segment PNDB. We demonstrate the effectiveness of the c onjugate-gradient. method in the design of DPE's that produce multiple -segment PNDB's in which two consecutive segments are separated by a d ark region along the optical axis. We also evaluate the degree of nonu niformity of the axial intensity over a given axial region. The design results match the requirements quite well. (C) 1998 Optical Society o f America.