Hybrid Metalens for Miniaturised Ultraviolet Fluorescence Detection

The advantages of metalenses to enable miniaturized systems have been well established, especially in the visible and infrared wavelength regimes. ultraviolet (UV) presents a final frontier because feature size scales as wavelength, so realizing large metalens with high numerical aperture (NA) UV is major challenge. Here, single-layer, thin-film (450 nm) hybrid an NA 0.9 diameter 6.2 mm presented. By combining Fresnel lens optimised binary gratings, well-known shadowing effect lenses at avoided while being able realize area lens. It demonstrated that combination affords efficient detection tryptophan-like fluorescence, which well-studied proxy for water contamination faecal coliforms. tryptophan levels better than 1 ppb, corresponds low-risk category drinking according World Health Organization (WHO), shown. also confirmed fluorescence collection efficiency 3.5 times higher plano-convex used state-of-the-art fluorometers, demonstrates versatile approach opens up new opportunities UV.