Journal
OPTICS EXPRESS
Volume 17, Issue 7, Pages 5330-5339Publisher
OPTICAL SOC AMER
DOI: 10.1364/OE.17.005330
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- Materials and Chemical Research Laboratory of the Industrial Technology Research Institute (ITRI)
- Taiwan's National Science Council [NSC 97-2221-E-002-159-MY3]
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We examined the optical properties such as propagation modes, focal length, side lobes, etc. of metallic subwavelength annular apertures (SAA) and used finite-difference time-domain (FDTD) simulation to compare our experimental findings. Using two different metals, silver and tungsten, we examined the different optical transmission properties of the two metallic SAA structures. The far-field propagation of the silver SAA structure was found to be a type of quasi-Bessel beam when compared with a quasi-Bessel beam generated by a perfect axicon. The propagation characteristics of these two beams were found to match qualitatively. The far-field transmitted light generated by the silver SAA structure was found to possess a 390nm sub-micron focal spot with a 24 mu m depth of focus, which was much smaller than the focal spot generated by a perfect axicon. We also found that a silver SAA structure can generate a sub-micron quasi-Bessel beam that has a much lower far-field side-lobe when compared to that of non-diffraction beams generated by a tungsten SAA structure. (C) 2009 Optical Society of America
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