Hindawi Publishing Corporation Advances in Optical Technologies Volume 2012, Article ID 974281, 11 pages doi:10.1155/2012/974281 Research Article Near-Field Diffraction from a Binary Microaxicon Victor V. Kotlyar, 1, 2 Sergey S. Stafeev, 1, 2 Roman V. Skidanov, 1, 2 and Victor A. Soifer 1, 2 1 Laser Measurements Laboratory, Image Processing Systems Institute, The Russian Academy of Sciences, 151 Molodogvardeyskaya Street, Samara 443001, Russia 2 Technical Cybernetics Subdepartment, S. P. Korolyov Samara State Aerospace University, 34 Moskovskoe Shosse, Samara 443086, Russia Correspondence should be addressed to Sergey S. Stafeev, sergey.stafeev@gmail.com Received 5 April 2012; Accepted 7 June 2012 Academic Editor: Maria Calvo Copyright © 2012 Victor V. Kotlyar et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We study binary axicons of period 4, 6, and 8 μm fabricated by photolithography with a 1 μm resolution, 500 nm depth, and 4 mm diameter. Near-field diffraction focal spots varying in diameter from 3.5λ to 4.5λ (for the axicon of period T = 4 μm) and from 5λ to 8λ (for the axicon with T = 8 μm) are experimentally found on the optical axis at a distance of up to 40 μm from the axicon for the wavelength λ = 0.532 μm. The first focal spot is found at distance 2 μm(T = 4 μm), with the period of the focal spots being 2 μm(T = 4 μm) and 4 μm(T = 8 μm). 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 T = 4 μm 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 μm and thickness 3 μm, combined with a lens of radius 70 μm was used for generating a Bessel beam of diameter 20 μm maintained over 500 μm distance at wavelength λ = 1.55 μm. 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, n = 3.13; radius of the rods, 0.22a; wavelength, λ = a/ 0.36, where a is the period of the rod array. A diverging Bessel beam of diameter FWHM = 1.5λ at half-maximum intensity was shown to be generated at a distance of z< 30a. 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 (λ = 532 nm), a conical axicon, and an immersion microlens with numerical aperture NA =1.25 found in a silver film of thickness 50 nm (permittivity ε = −10.1786 − i0.8238). The central axial ring diameter was 278 nm and the thickness was 250 nm ≈ 0.5λ. The surface plasmon pattern was observed with a near-field microscope Veeco Aurora 3 with a 50–100nm resolution. In a similar work [7], a scheme including a radially polarized beam of a He-Ne laser (λ = 632.8 nm), an axicon, and an immersion lens with NA = 1.4 in a 44nm thick Au film (ε = 0.3+ i3.089) was used to form a surface plasmon with a central focal spot of diameter FWHM = 0.22 μm = 0.35λ. The plasmon was observed with the aid of a latex ball 175 nm in diameter. Focusing the laser light in the neighborhood of an annular structure on metal was discussed in [8, 9]. In [8], the focusing of light with a zone plate of the ring radii r n 2 = 2nfλ + n 2 λ 2 , f = 1 μm, λ = 633 nm, was simulated by the FDTD method. The plate was realized in thin silver (50 nm) and golden (50 nm) films deposited on silica. The diameter of the ring array was 13 μm. A focal spot of half- intensity diameter FWHM = 0.3λ (spot’s full width being 0.7λ) was shown to occur at a distance of z = 1.5 μm