Yellow whispering-gallery-mode lasing from amorphous fluoride microspheres

TL;DR

This paper introduces a novel visible microlaser platform using amorphous fluoride microspheres doped with dysprosium, achieving low-threshold whispering-gallery-mode lasing in the yellow spectrum with high quality factors.

Contribution

The work demonstrates the first fiber-coupled whispering-gallery-mode lasing from amorphous fluoride microspheres, expanding visible laser sources with low noise and tunability.

Findings

Achieved yellow WGM lasing at 573 nm with a threshold of 190 μW.

Demonstrated a high quality factor of 3.5 million.

Showcased potential for broad spectral coverage and fiber-based amplification.

Abstract

Compact, low-noise coherent light sources in the visible remain challenging due to limited gain platforms and inefficient pumping. We report a new route to visible microlasing based on direct, one-photon blue pumping and an amorphous fluoride gain material platform. Dysprosium doped fluoride microspheres are fabricated via plasma-torch-induced, pressureless amorphization of single crystals, enabling compositions beyond conventional glass-forming limits while ensuring ultrasmooth morphology, low phonon energy, and homogeneous dopant distribution. We demonstrate the first fiber-coupled whispering-gallery-mode lasing from an amorphous fluoride microsphere in the yellow (573 nm), with an ultralow threshold of $190 \mu$W despite spin-forbidden Dy$^{3+}$ transitions. Lasing is evidenced by characteristic light-light curve indicating a low spontaneous emission factor, narrow-linewidth emission, and relaxation oscillations yielding a loaded quality factor of $Q = 3.5 \times 10^6$. This platform is readily extendable to other rare-earth emitters, enabling entire visible spectral coverage beyond the limitations of upconversion pumping, with prospects for color-tunable and white-light emission. Finally, fiber-based amplification of the WGM signal demonstrates a pathway toward compact, fiber-integrated visible microlasers with controllable noise and linewidth.