Abstract
Lens-based optical microscopes cannot resolve the sub-wavelength objects overpass diffraction limit. Recently, research on super-resolution imaging has been conducted to overcome this limitation in visible wavelength using solid immersion lenses. However, IR imaging, which is useful for chemical imaging, bio-imaging, and thermal imaging, has not been studied much in optical super-resolution by solid immersion lens owing to material limitations. Herein, we present the design and fabrication schemes of microscale silicon solid immersion lenses (µ-SIL) based on thin-film geometry for mid-infrared (MIR) applications. Compared with geometrical optics, a rigorous finite-difference time-domain (FDTD) calculation of proposed silicon microlenses at MIR wavelengths shows that the outstanding short focal lengths result in enhanced magnification, which allows resolving objects beyond the diffraction limit. In addition, the theoretical analyses evaluate the influences of various structural parameters, such as radius of curvature (RoC), refractive index, and substrate thickness, in µ-SIL. In particular, the high refractive index of µ-SIL is beneficial to implement the outstanding near-field focusing, which corresponds to a high numerical aperture. On the basis of this theoretical background, novel methods are developed for the fabrication of a printable, thin-film silicon microlens array and its integration with a specimen substrate. From the result, we provide a physical understanding of near-field focusing phenomena and offer a promising tool for super-resolution far-field imaging in the MIR range.
Highlights
As the resolution of a standard lens-based optical microscope imaging system is limited by diffraction to about half of the illumination wavelength, overcoming this resolution limit has been one of the primary interests in many areas of scientific and engineering research, such as nanophotonics, biochemical imaging, and material science [1,2,3,4]
ResFuigltusraen3da,Db igsrcaupshsiiocanlly show the effect of the refractive index of μ-solid immersion lens (SIL) on the focal length
We performed a numerical simulation to investigate the focal properties of μ-SILs in the MIR band, analyzing the dependence of the shape, radius of curvature (RoC), and refractive index as a promising tool for far-field imaging beyond the optical diffraction limit
Summary
As the resolution of a standard lens-based optical microscope imaging system is limited by diffraction to about half of the illumination wavelength, overcoming this resolution limit has been one of the primary interests in many areas of scientific and engineering research, such as nanophotonics, biochemical imaging, and material science [1,2,3,4]. Diverse studies of numerical calculations and experimental results have reported that far-field imaging beyond the optical diffraction limit can be achieved in real time only through the use of a conventional optical microscope with a wavelength-scale solid immersion lens (SIL) or a dielectric microsphere in close contact with the specimen of interest [5,6,7,8,9,10]. MicromaIcRhiniems 2a0g2i0n, 1g1, i2s50widely used for a broad range of applications including thermal imagi2nogf,8 biochemical imaging, and basic scientific research [11,12,13].
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