On focusing of a converging spherical wave traveling through the boundary of a material medium

详细

It is revealed in the ray approximation that focusing of a converging spherical wave traveling through the boundary of a material medium can be retained if a lens-like pad is used on the medium boundary. Conditions imposed on the parameters of such a pad are presented. Dimensions of the volumetric spot in the region of the wave focusing point are estimated with consideration for the Fraunhofer diffraction at the edge of a round pad.