Abstract
Based on the radial finite-difference time domain method we numerically show that the illumination of a conical glass microaxicon of base radius and height (numerical aperture ) by a radially polarized annular laser mode of wavelength produces, 20 nm apart from the cone apex, a sharp focus of transverse diameter and longitudinal (axial) width . The focal spot area at half-maximum intensity is . For comparison the focus diameter reported here is 1.7 times smaller than the diameter of the minimal diffraction spot (Airy disk, ) of , with its area being 2.87 times smaller than that of the Airy disk . Also it is smaller than the diameter of a focal spot formed by a lens with in an immersion medium , , smaller than the diffraction limit in the medium (, ) and smaller than the focusing limit for the Bessel beam .
© 2010 Optical Society of America
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