High refractive index immersion liquid for super-resolution 3D imaging using sapphire-based aNAIL optics

TL;DR

This paper introduces a new high refractive index immersion liquid made from antimony tribromide in diiodomethane, enabling improved sapphire-based optics for deep 3D super-resolution imaging.

Contribution

The authors develop a tunable high refractive index immersion liquid that matches sapphire, enhancing the performance of aNAIL optics for deep 3D imaging.

Findings

Refractive index tunable from 1.74 to 1.873

Excellent light transmittance across UV to near-IR

Enabled sapphire-based aNAIL with NA=1.17 and 12mm working distance

Abstract

Optically-transparent immersion liquids with refractive index (n ~ 1.77) to match sapphire-based aplanatic numerical aperture increasing lens (aNAIL) are necessary for achieving deep 3D imaging with high spatial resolution. We report that antimony tribromide (SbBr$_{3}$) salt dissolved in liquid diiodomethane (CH$_{2}$I$_{2}$) provides a new high refractive index immersion liquid for optics applications. The refractive index is tunable from n = 1.74 (pure) to n = 1.873 (saturated), by adjusting either salt concentration or temperature; this allows it to match (or even exceed) the refractive index of sapphire. Importantly, the solution gives excellent light transmittance in the ultraviolet to near-infrared range, an improvement over commercially-available immersion liquids. This refractive index matched immersion liquid formulation has enabled us to develop a sapphire-based aNAIL objective that has both high numerical aperture (NA = 1.17) and long working distance (WD = 12 mm). This opens up new possibilities for deep 3D imaging with high spatial resolution.