KEYWORDS: Plasmonics, Scanning electron microscopy, Transmittance, Silver, Nanofabrication, Metals, Near field, Near field scanning optical microscopy, CCD cameras, Imaging systems
To learn about the challenges, difficulties and technological steps in fabrication of a metal lens, a cascaded plasmonic
superlens was fabricated in this paper and then its subwavelength imaging capability is demonstrated. First, we
developed separately the fabrication and characterization procedures for each part in the cascaded superlens structure
(composed of a planar plasmonic lens and a double layer meander structure) to show the precise fabricating process and
results. Then the two parts of the cascaded structure were stacked together on the top of a double-slit object. First a larger
slit width of 400 nm and a slit distance of 800 nm were used for easily obtaining a larger transmittance intensity
distribution. The results show a good agreement between the experiment and simulation. Then a double-slit with width
of 100 nm and distance of 180 nm were used to further test the resolving power of the superlens. The captured images
show that the desired subwavelength resolution in the far field can be realized with the fabricated superlens.
KEYWORDS: Near field optics, Plasmonics, Near field, Nanoimaging, Optical imaging, Beam steering, Hyperlenses, Super resolution, Super resolution microscopy, Geometrical optics, Silver, Spectral resolution, Refractive index
Nano-imaging has imposed a fundamental impact on the development of nanoscience and technology. The demands for direct subwavelength imaging in far field have been significantly increased. Such a superlens needs first to be able to collect the near field information, and then transform it into the far field with magnification and low image distortion. In this contribution we demonstrate a superlens with a novel design for far field observation at visible wavelengths. The lens is based on a silicon half cylinder with several micrometers in size. Without any structuring, the silicon semicylinder can already work as a lens with high resolving power due to its high refractive index. A distance of 280 nm between two incoherent dipoles immersed in water can be well resolved at a wavelength of 640 nm. Deep subwavelength imaging with magnification can be achieved when the flat surface of the semi-cylinder is structured with periodic plasmonic grating. When a ridge of the grating is centered at the optical axis of the lens, a local magnification factor of 10 can be obtained and the smallest resolvable distance between two point dipoles in water is around 120 nm at 640 nm wavelength. Moreover, this superlens also works at other visible wavelengths with a similar performance.
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