Comparative modeling of sharp focusing with zone plate using two methods

We simulated a focusing of radially-polarized mode using two methods: FDTD and Richards-Wolf equations. It was shown that both methods demonstrate the ability of overcoming the diffraction limit using a zone plate with radius R = 20(lambda) and R-TEM01 mode with radius (omega) = 10(lambda). The overcoming of the diffraction limit was observed when numerical aperture of the zone plate was more than NA = 0.97 for FDTD-method and more than NA = 0.96 for Richards-Wolf equation. The relative error of the width of the focal spot was less than 6%.