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Updated: Jun 21, 2026

Single Plane Illumination Module and Micro-capillary Approach for a Wide-field Microscope
Published on: August 15, 2014
Continuous numerical aperture properties of a cylindrically polarized light illuminated sub-wavelength annular
Chun-Chieh Fang1, Tsung-Dar Cheng, Jyi-Tyan Yeh
1Institute of Applied Mechanics, National Taiwan University, Taipei, Taiwan.
Abstract:
We investigated the process of focusing a radially polarized (RP) light beam through a sub-wavelength annular aperture (SAA). We found that the result was a non-diffraction doughnut-shaped light beam which propagates in free space. After analyzing the electric field component of the focus generated by the SAA structure, we identified the relationship between the focal field generated by the SAA. We then compared it to a case with a traditional objective lens. From our findings, we propose that a SAA structure can be viewed as a continuous numerical aperture optical element.
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