TY - JOUR
T1 - Source Image Squeezing and Field Tunneling for Propagating Light Beyond-Limit Focusing to Reach the Intermediate Zone
AU - Hong, Jian Shiung
AU - Wang, Ting Kai
AU - Chen, Alexander Ewen
AU - Li, Hsiang nan
AU - Chen, Kuan Ren
N1 - Funding Information:
This work was supported by the Ministry of Science and Technology, Taiwan (Grant Numbers: 104-2112-M-006-004-MY3, 107-2112-M-006-011, 108-2112-M-006-014). Acknowledgments
Funding Information:
The authors are grateful for support from Ministry of Science and Technology and computational resources at National Center for High-performance Computing at National Applied Research Laboratories.
Publisher Copyright:
© 2020, Springer Science+Business Media, LLC, part of Springer Nature.
PY - 2021/4
Y1 - 2021/4
N2 - The physics for beyond-limit focusing has great academic importance, particularly for light propagation with control over focal point location and spot size. Asymmetric boundary confinement for a beyond-limit focusing lens in a metallic subwavelength structure redirects the surface current at the inner edges of the interface between an upstream double slit with width much smaller than the wavelength and a downstream slit with width close to one wavelength. This induces intense localized fields and tightly squeezes spatial distributions for the wave sources and corresponding images that are critical for focusing beyond the diffraction limit, as opposed to separated sources in super-oscillatory lenses and metalenses for optically large areas. This squeezing simultaneously increases the distance between source and image peaks and reduces their distribution widths one order less than the wavelength. The corresponding spatial spectrum alters to excite an inward-propagation wave mode with strong lateral wave momentum for focusing. The radiated inward propagation wave mode can be manipulated to help the focused field tunnel through the downstream slit, such that the focal point can reach the intermediate zone. Source and image radiation confirmed that focused field propagation had good agreement with simulation results. The proposed analytical Green’s method opens new physics applications for this fundamental focusing process, offering new opportunities to further reduce spot size and tailoring the focal length for important potential plasmonic applications.
AB - The physics for beyond-limit focusing has great academic importance, particularly for light propagation with control over focal point location and spot size. Asymmetric boundary confinement for a beyond-limit focusing lens in a metallic subwavelength structure redirects the surface current at the inner edges of the interface between an upstream double slit with width much smaller than the wavelength and a downstream slit with width close to one wavelength. This induces intense localized fields and tightly squeezes spatial distributions for the wave sources and corresponding images that are critical for focusing beyond the diffraction limit, as opposed to separated sources in super-oscillatory lenses and metalenses for optically large areas. This squeezing simultaneously increases the distance between source and image peaks and reduces their distribution widths one order less than the wavelength. The corresponding spatial spectrum alters to excite an inward-propagation wave mode with strong lateral wave momentum for focusing. The radiated inward propagation wave mode can be manipulated to help the focused field tunnel through the downstream slit, such that the focal point can reach the intermediate zone. Source and image radiation confirmed that focused field propagation had good agreement with simulation results. The proposed analytical Green’s method opens new physics applications for this fundamental focusing process, offering new opportunities to further reduce spot size and tailoring the focal length for important potential plasmonic applications.
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U2 - 10.1007/s11468-020-01319-z
DO - 10.1007/s11468-020-01319-z
M3 - Article
AN - SCOPUS:85096054457
SN - 1557-1955
VL - 16
SP - 619
EP - 628
JO - Plasmonics
JF - Plasmonics
IS - 2
ER -