Using immersion lenses is a common approach to enhance the resolving power in various fields of optics such as microscopy and lithography. However, conventional immersion lenses are bulky, high-cost and are typically designed for only a few specific immersion liquids. The development of meta-surfaces provides a promising approach to manipulate light in a compact configuration, enabling many optical devices such as polarizers, waveplates and lenses. These are mainly focused in the near-infrared or the long-wavelength region of the visible spectrum due to fabrication challenges and intrinsic losses of materials used. Here, we demonstrate oil immersion planar lenses with a numerical aperture of 1.1 at visible wavelengths. The lenses provide diffraction-limited focal spots with Strehl ratios higher than 0.9 and 0.8 at their design wavelengths of 532 nm and 405 nm, respectively. Fabrication is based on an atomic-layer deposition (ALD) of TiO2. The loss of TiO2 in the visible is negligible and the surface roughness is well-controlled due to the precise monolayer growth of the TiO2 film. By applying the lens (designed at 532 nm) in a confocal scanning microscopy setup, we are able to achieve high-quality images with sub-wavelength resolution. It should be noted that this lens can be efficiently tailored for any liquid. We demonstrate another design for water-immersion lenses, which are highly applicable to super-resolution bio-imaging applications. The compactness and design flexibility of this platform is highly promising for widespread applications in imaging and spectroscopy.
Wei Ting Chen, Alexander Y. Zhu, Mohammadreza Khorasaninejad, Zhujun Shi, Jaewon Oh, Robert C. Devlin, and Federico Capasso, "Planar dielectric metasurfaces for immersion optics (Conference Presentation)," Proc. SPIE 10112, Photonic and Phononic Properties of Engineered Nanostructures VII, 101120M (Presented at SPIE OPTO: January 31, 2017; Published: 28 April 2017); https://doi.org/10.1117/12.2258541.5395679899001.
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