| Abstract: | We discuss the feasibility of generating focal areas in different diffraction fields and prove that the term ‘diffraction-free’ beams is used to designate a spatially limited portion of the toroidal light wave. The light line, or axial caustic, is a result of interference of intersecting areas of this wave. It is shown that the ‘diffraction-free’ beams are generated by such optical elements whose phase transmission function includes linear terms with respect to the radial coordinate. A comparison of optical characteristics of caustics in the near- and far-diffraction fields is made. Synthesis of a new diffraction-modulated axicon that forms two focal areas of different types is reported. The results of experimental studies of its optical characteristics are discussed. |
