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Comparison of SOL and ONSOL. The SOL produces a complex pattern of spots and sidebands at different distances for the lens. The ONSOL produces a much simpler pattern with a subwavelength needle on the optical axis and sidebands far from the axis.
Designs ((a)–(c)) and SEM images ((d)–(f)) of the of the lenses. (a) and (d) SOL, (b) and (e) ONSOL with 20 μm diameter opaque region, (c) and (f) control sample; 20 μm diameter Au disk in a 70 μm diameter transparent region.
Experimental ((a)–(c)) and simulated ((d) and (e)) intensity of the lens interference patterns. (a) and (d) SOL, (b) and (e) ONSOL with 20 μm diameter opaque region, (c) and (f) disc control sample. The colour scale in plots (c) and (f) has been adjusted to improve the visibility of the very low intensity spots.
Distribution of FWHM and axial intensity (in arbitrary units) with propagation distance away from the lens for (a) the SOL, (b) the ONSOL; each figure on the right hand side shows the corresponding zoomed-in view from 0 to 10 μm. The simulated FWHM of the disc spot is shown in (b) by the dashed line.
Focal spots at (a) z = 5.7 μm for the SOL and at (c) z = 5.9 μm for the ONSOL. (b) and (d) show intensity profiles through the lines in (a) and (c), respectively.
Simulated optical needles formed by ONSOLs with various diameters of the blocking region. The length of the needle increases with the diameter of the blocking region and the needle moves further from the ONSOL, but the intensity of the needle reduces.
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