Diffraction of laser beam on a two-zone cylindrical microelement

Analytically and numerically shown, that an optical microelement consisting just two cylindrical zones is useful for sharp focusing of laser radiation if the radius of the central zone is halfwavelength. The numerical calculations executed in approach of a thin element by means of the plane wave expansion method show good accordance with analytical estimations. Also the qualitative accordance is shown on the basis of finite-difference time-domain method in view of three-dimensional structure of an element. Characteristics and features of diffraction of Gaussian beam with linear and circular polarization on a considered element are investigated.