University of Waterloo , Waterloo, Ontario N2L 3G1, Canada.
Nano Lett. 2017 May 10;17(5):3188-3194. doi: 10.1021/acs.nanolett.7b00717. Epub 2017 Apr 13.
Immersion objectives can focus light into a spot smaller than what is achievable in free space, thereby enhancing the spatial resolution for various applications such as microscopy, spectroscopy, and lithography. Despite the availability of advanced lens polishing techniques, hand-polishing is still required to manufacture the front lens of a high-end immersion objective, which poses major constraints for lens design. This limits the shape of the front lens to spherical. Therefore, several other lenses need to be cascaded to correct for spherical aberration, resulting in significant challenges for miniaturization and adding design complexity for different immersion liquids. Here, by using metasurfaces, we demonstrate liquid immersion meta-lenses free of spherical aberration at various design wavelengths in the visible spectrum. We report water and oil immersion meta-lenses of various numerical apertures (NA) up to 1.1 and show that their measured focal spot sizes are diffraction-limited with Strehl ratios of approximately 0.9 at 532 nm. By integrating the oil immersion meta-lens (NA = 1.1) into a commercial scanning confocal microscope, we achieve an imaging spatial resolution of approximately 200 nm. These meta-lenses can be easily adapted to focus light through multilayers of different refractive indices and mass-produced using modern industrial manufacturing or nanoimprint techniques, leading to cost-effective high-end optics.
浸没目标可以将光聚焦到比自由空间中更小的光斑，从而提高各种应用的空间分辨率，例如显微镜、光谱学和光刻。尽管有先进的透镜抛光技术，但仍然需要手工抛光来制造高端浸没物镜的前透镜，这对透镜设计构成了重大限制。这将前透镜的形状限制为球形。因此，需要级联几个其他透镜来校正球差，从而导致小型化和不同浸没液体的设计复杂性增加。在这里，我们使用超表面展示了在可见光谱的各种设计波长处没有球差的液体浸没超透镜。我们报告了各种数值孔径（NA）的水和油浸没超透镜，高达 1.1，并表明它们的测量焦斑尺寸在 532nm 处具有衍射极限的光斑大小，斯特列尔比约为 0.9。通过将油浸超透镜（NA = 1.1）集成到商用扫描共焦显微镜中，我们实现了约 200nm 的成像空间分辨率。这些超透镜可以轻松适应通过不同折射率的多层聚焦光，并且可以使用现代工业制造或纳米压印技术进行批量生产，从而实现经济高效的高端光学器件。
