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Metalens for energy backflow

Using electronic beam lithography and ion etching we manufactured a metalens with diameter 30 μm, focal length 633 nm and relief depth of 130 nm. The metalens consists from 16 sector subwavelength binary gratings with period 220 nm. The proposed metalens generates a left-hand circularly polarized optical vortex with topological charge 2 when it is illuminated by left-hand circularly polarized light; however, it generates a cylindrical vector beam of the second order when it is illuminated by linearly polarized light. In both cases a region of inverse energy flow occurs in the focal spot.