Super-Resolution Imaging With Fluorotellurite Glass Microspheres

Microsphere-lens-assisted optical nanoscopy has emerged as a powerful approach for surpassing the diffraction limit of conventional optical microscopy. Here, we present a comprehensive investigation of high-refractive-index fluorotellurite (TeO₂-BaF₂-Y₂O₃, TBY) glass microspheres fabricated by a high-temperature floating-zone melting technique. The microspheres exhibit excellent sphericity, ultra-smooth surfaces, diameters from 10 to 200 μm, a refractive index of ∼1.9, and up to 85% visible transmittance. Ray-tracing and full-wave electromagnetic simulations qualitatively and quantitatively characterize their near-field focusing and efficient evanescent-to-propagating wave conversion. When fully embedded in a PDMS matrix, TBY microspheres enabled super-resolution imaging of anodic aluminum oxide and other nanoscale samples, resolving features down to 50 nm and attaining a maximum magnification of ∼4.34× on 100 nm grating structures. We show that image-plane selection and precise axial alignment critically influence image clarity, contrast, and magnification, and we systematically investigate these trade-offs across sphere diameters. An ultramicroscopic objective (UO) module integrating a plano-convex lens with an embedded microsphere was developed to provide micrometer-precise positioning, reusability, and straightforward compatibility with commercial microscopes. The high near-infrared transmittance, low dispersion, and thermal stability of fluorotellurite glass indicate promising applications in deep-tissue near-infrared super-resolution, multi-band spectroscopic nanoscopy, and laser micro-machining.