Two-petal laser beam near a binary spiral axicon with topological charge 2

Abstract

We were the first to notice that although in the immediate vicinity of a spiral axicon with m > 0 there is no light ring, there is an intensity pattern composed of several intensity petals, whose number is equal to the axicon topological charge, m. We experimentally demonstrate that a spiral axicon with the topological charge m = 2 and numerical aperture NA ≈ 0.6, operating at a 532-nm wavelength and fabricated by electron lithography, generates a two-petal (TP) laser beam rotating in the near-field (several micrometers away from the microaxicon surface). The rotation rate attained is higher than any that has been reported to date. It is worth noting that the higher the rotation rate of the TP-beam, the higher the axial resolution of an optical system that can be achieved without increasing its NA. Because a small on-axis shift of a point object leads to a large angle of rotation of its TP-image.