Formulation and application of the finite-difference time-domain method for the analysis of axially symmetric diffractive optical elements

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Abstract
We formulate and apply an efficient finite-difference time-domain algorithm to the analysis of axially symmetric diffractive optical elements. We discuss aspects relating to minimizing numerical dispersion in the incident field, application of absorbing boundary conditions in the radial direction, convergence to a steady state, and propagation of the steady-state electromagnetic fields from the finite-difference time-domain region to the plane of interest. Incorporation of these aspects into a single finite-difference time-domain algorithm results in an extremely efficient and robust method for diffractive optical element analysis. Application to the analysis of subwavelength and multilevel lenses, both with and without loss, for focusing planar and Gaussian beams is presented.