# Super‐Resolution Imaging With Fluorotellurite Glass Microspheres

## TL;DR

Researchers developed fluorotellurite glass microspheres to enable super-resolution imaging and precise nanoscale observation.

## Contribution

High-refractive-index fluorotellurite glass microspheres are fabricated and integrated into imaging systems for enhanced super-resolution capabilities.

## Key findings

- Fluorotellurite microspheres achieved 50 nm resolution and 4.34× magnification on 100 nm gratings.
- The microspheres enabled efficient evanescent-to-propagating wave conversion and stable imaging in a PDMS matrix.
- An ultramicroscopic objective module was developed for precise positioning and compatibility with commercial microscopes.

## Abstract

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.

Microsphere lenses made from fluorotellurite glass with a high refractive index and excellent transparency were used to develop a super‐resolution imaging technique and ultramicroscopic objective modules. This approach enables efficient, stable, and precisely controllable imaging with broad potential in life sciences and nanotechnology.