# Inner structure of ZnO microspheres fabricated via laser ablation in superfluid helium

## TL;DR

This study investigates the internal structure of ZnO microspheres created by laser ablation in superfluid helium, revealing voids that do not affect optical whispering gallery modes, and suggests their formation mechanism.

## Contribution

It provides the first detailed analysis of the internal voids in ZnO microspheres fabricated in superfluid helium, linking void formation to the fabrication process.

## Key findings

- Void-like bubbles are present inside ZnO microspheres.
- Void location does not significantly affect whispering gallery modes.
- Presence of voids indicates helium or evaporated material was trapped during formation.

## Abstract

ZnO microspheres fabricated via laser ablation in superfluid helium were found to have bubble-like voids. Even a microsphere demonstrating clear whispering gallery mode resonances in the luminescence had voids. Our analysis confirmed that the voids are located away from the surface and have negligible or little effect on the whispering gallery mode resonances since the electromagnetic energy localizes near the surface of these microspheres. The existence of the voids indicates that helium gas or any evaporated target material was present within the molten microparticles during the microsphere formation.