A Metalens with Near-Unity Numerical Aperture

• Published in: arXiv.org
• Main Authors: Paniagua-Dominguez, Ramon, Ye Feng Yu, Khaidarov, Egor, Choi, Sumin, Leong, Victor, Bakker, Reuben M, Liang, Xinan, Yuan Hsing Fu, Valuckas, Vytautas, Krivitsky, Leonid A, Kuznetsov, Arseniy I
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 10.01.2018
• Subjects: Aperture; Color centers; Diamonds; Lenses; Light refraction; Mapping; Microscopes; Nanocrystals; Numerical aperture; Optical components; Optics; Physics - Optics
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1705.00895

The numerical aperture (NA) of a lens determines its ability to focus light and its resolving capability. Having a large NA is a very desirable quality for applications requiring small light-matter interaction volumes or large angular collections. Traditionally, a large NA lens based on light refraction requires precision bulk optics that ends up being expensive and is thus also a specialty item. In contrast, metasurfaces allow the lens designer to circumvent those issues producing high NA lenses in an ultra-flat fashion. However, so far, these have been limited to numerical apertures on the same order of traditional optical components, with experimentally reported values of NA <0.9. Here we demonstrate, both numerically and experimentally, a new approach that results in a diffraction limited flat lens with a near-unity numerical aperture (NA>0.99) and sub-wavelength thickness (~{\lambda}/3), operating with unpolarized light at 715 nm. To demonstrate its imaging capability, the designed lens is applied in a confocal configuration to map color centers in sub-diffractive diamond nanocrystals. This work, based on diffractive elements able to efficiently bend light at angles as large as 82{\deg}, represents a step beyond traditional optical elements and existing flat optics, circumventing the efficiency drop associated to the standard, phase mapping approach.