Triple-wavelength lasing at 1.50 μm, 1.84 μm and 2.08 μm in a Ho³⁺/Tm³⁺ co-doped fluorozirconate glass microsphere

Simultaneous 1.50 μm, 1.84 μm and 2.08 μm laser emission is observed in a Ho³⁺/Tm³⁺ co-doped ZrF₄–BaF₂–YF₃–AlF₃ (ZBYA) fluoride glass microsphere when pumped using a 793 nm laser diode. The ZBYA fluoride glass microsphere was prepared using a CO₂ laser heating method and whispering-gallery modes (WGM) were excited when the pump light was coupled using a tapered fiber. The introduction of Ho³⁺ ions reduced the population of the long-lived Tm³⁺:³F₄ level and removed the ³H₄→ ³F₄ self-termination effect, resulting in the population of the Ho³⁺:⁵I₇ level through a resonant energy transfer process. As the 793 nm laser pump power grows, lasing occurs initially at 2.08 μm, followed by the cascade outputs at 1.50 μm and 1.84 μm.