Abstract
The presence of absorption losses softens the singular behavior of transmission resonances and leads to a good image in spite of limited effective spatial frequency range. Nonetheless, we found that the phase singularity does not disappear despite the considerably reduced retardation effects by softening the transmission resonances. Because the phase singularity severely deteriorates the ideal image reconstruction, broad transmission bandwidth in spatial frequency domain is not sufficient enough to achieve superresolution in TiO(2) thin film lens. The present work predicts successful elimination of the phase singularity and the achievement of approximately lambda /12.9 superresolution in TiO(2) thin film lens through the phase correction method.
Highlights
For the applications in photolithography and optical imaging, there have been extensive efforts to overcome the diffraction limit by developing negative index materials in various wavelength region from microwave to visible light [1,2,3,4,5,6]
To acquire the superresolution with the near-field superlens (NFSL), the real part (ε ) of permittivity is required to be negative for single negative index materials
The negative ε for superlensing effect is obtained by plasmonic oscillations of metals in the visible wavelength [7] and by lattice vibrations of dielectric polar crystals such as ZnSe, SiC, TiO2 and InP [8] in the mid infrared wavelength
Summary
For the applications in photolithography and optical imaging, there have been extensive efforts to overcome the diffraction limit by developing negative index materials in various wavelength region from microwave to visible light [1,2,3,4,5,6]. A delicate change in μ(ε) excites the coupled surface modes and leads to large transmission resonances in the spatial frequency domain, which cause Fourier components to be a broad background ‘noise’ in the image [16, 17] These retardation effects severely limit the image resolution and stimulate the excitation of slab resonances that degrade the performance of the lens. We recognize that the phase singularity persists despite the reduced retardation effects by softening the singular behavior of transmission resonances Because this phase singularity significantly prevents the ideal image reconstruction, TiO2 thin-film lens, as an example, has not been considered as a NFSL candidate even though the transmission has enough broad bandwidth for superresolution in the spatial frequency domain.
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