%0 Journal Article
%T Near-Field Diffraction from a Binary Microaxicon
%A Victor V. Kotlyar
%A Sergey S. Stafeev
%A Roman V. Skidanov
%A Victor A. Soifer
%J Advances in Optical Technologies
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/974281
%X We study binary axicons of period 4, 6, and 8£¿¦Ìm fabricated by photolithography with a 1£¿¦Ìm resolution, 500£¿nm depth, and 4£¿mm diameter. Near-field diffraction focal spots varying in diameter from 3.5¦Ë to 4.5¦Ë (for the axicon of period £¿¦Ìm) and from 5¦Ë to 8¦Ë (for the axicon with £¿¦Ìm) are experimentally found on the optical axis at a distance of up to 40£¿¦Ìm from the axicon for the wavelength £¿¦Ìm. The first focal spot is found at distance 2£¿¦Ìm ( £¿¦Ìm), with the period of the focal spots being 2£¿¦Ìm ( £¿¦Ìm) and 4£¿¦Ìm ( £¿¦Ìm). Diffraction of linearly polarized plane and diverging waves is simulated using FullWAVE (RSoft) and a proprietary program BOR-FDTD, which implement finite-difference schemes to solve three-dimensional Maxwell's equations in the Cartesian and cylindrical coordinates. The numerically simulated values for diameters of the near-field focal spots for the axicon of period £¿¦Ìm are in good agreement with the experimental values. 1. Introduction Axicons [1] are known to be suitable for generating a diffraction-free laser Bessel beam in a definite range of the optical axis [2, 3]. Such beams continue to attract researchers¡¯ interest. In [4] a coreless silica fiber of diameter 30£¿¦Ìm and thickness 3£¿¦Ìm, combined with a lens of radius 70£¿¦Ìm was used for generating a Bessel beam of diameter 20£¿¦Ìm maintained over 500£¿¦Ìm distance at wavelength £¿¦Ìm. In [5] the FDTD-method was used to model a 2D photonic crystal composed of an axicon-shaped rectangular array of dielectric rods: axicon base, 20a; height, 10a; refractive index of the rods, ; radius of the rods, 0.22a; wavelength, , where a is the period of the rod array. A diverging Bessel beam of diameter ¦Ë at half-maximum intensity was shown to be generated at a distance of a. A surface plasmon wave in the form of concentric rings described by the first-order Bessel function was reported in [6] in experiments using a radially polarized laser beam ( £¿nm), a conical axicon, and an immersion microlens with numerical aperture 1.25 found in a silver film of thickness 50£¿nm (permittivity ). The central axial ring diameter was 278£¿nm and the thickness was . The surface plasmon pattern was observed with a near-field microscope Veeco Aurora 3 with a 50¨C100£¿nm resolution. In a similar work [7], a scheme including a radially polarized beam of a He-Ne laser ( £¿nm), an axicon, and an immersion lens with in a 44£¿nm thick Au film ( ) was used to form a surface plasmon with a central focal spot of diameter ¦Ë. The plasmon was observed with the aid of a latex ball 175£¿nm in diameter. Focusing the laser light in the
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