Polarization filtering with isomaterial multifocal metalenses at ultraviolet frequencies

The growing demand for complex nanophotonic devices that operate in the ultraviolet (UV) range necessitates the development of innovative compatible optical devices, particularly for use in lithography applications. In this context, we introduce the first non-contrast dielectric flat metalenses that offer tunable multi-focal polarization channeling in the UV region. The metalens we have developed consists of equally spaced Al\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document}O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_3$$\end{document} nanoblocks carved on an Al\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document}O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_3$$\end{document} substrate. We demonstrate that controlling the arrangement of nanoblocks on the substrate provides a sufficient geometric phase (Pancharatnam-Berry phase) for developing spatially tunable quadruple-focal metalens in the UV region. While illuminating with the linear polarized light, precise manipulation of the phase profile generates multiple tightly confined focal points, where each possesses different controllable circular polarization states. This feature makes the offered approach a suitable strategy for spatially controlled polarization filtering and channeling. Our design also shows high polarization conversion efficiency in the whole UV spectrum. As proof of concept, we show the focusing characteristics of our designed metalens at four chosen wavelengths. This study demonstrates a promising basis for further development of UV nanophotonic devices and potentially opens up new opportunities for future employment of flat optics in a variety of industrial applications in the UV range.