Journal
NANOMATERIALS
Volume 12, Issue 20, Pages -Publisher
MDPI
DOI: 10.3390/nano12203553
Keywords
superlens; subwavelength imaging; optical transfer function; planar waveguide; surface plasmon polaritons
Categories
Funding
- Shanghai Pujiang Program [20PJ1418600]
- Henan Provincial Major Project of Science and Technology [221100210200]
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A double-layer metal superlens was designed to improve subwavelength imaging ability. The transmission properties of the imaging system were accurately interpreted using waveguide mode theory. By amplifying high spatial frequency evanescent waves and diminishing low spatial frequency evanescent waves, a flat and broad optical transfer function was achieved, improving the subwavelength imaging performance.
A double-layer metal superlens was rigorously analyzed and systematically designed to improve subwavelength imaging ability. It was revealed that transmission properties of the imaging system could be accurately interpreted by the five-layer waveguide mode theory-each amplification peak among the spatial frequency range of evanescent waves was associated with a corresponding surface plasmon polariton (SPP) mode of an insulator-metal-insulator-metal-insulator (IMIMI) structure. On the basis of such physical insight, evanescent waves of higher spatial frequency were effectively amplified via increasing propagation constants of symmetrically coupled short-range SPP (s-SRSPP) and antisymmetrically coupled short-range SPP (a-SRSPP), and evanescent waves of lower spatial frequency were appropriately diminished by approaching to cut off symmetrically coupled long-range SPP (s-LRSPP). A flat and broad optical transfer function of the imaging system was then achieved, and improved subwavelength imaging performance was validated by imaging an ideal thin object of two slits with a 20-nm width distanced by a 20-nm spacer, under 193-nm illumination. The resolution limit of the designed imaging system with double-layer superlens was further demonstrated to be at least similar to lambda/16 for an isolated two-slit object model. This work provided sound theoretical analysis and a systematic design approach of double-layer metal superlens for near-field subwavelength imaging, such as fluorescent micro/nanoscopy or plasmonic nanolithography.
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