Quenching of $3.4~\mu \text{m}$ Dual-Wavelength Pumped Erbium Doped Fiber Lasers

We report on a quenching behavior of the 3.4 μm dual-wavelength pumped fiber laser that can be accounted by the adverse contribution from a new excited state absorption transition in Er
³⁺
:ZrF
₄
glasses. The transition occurs between levels
⁴
F
_9/2
and
⁴
F
_7/2
and partially overlaps with the 1976 nm pump wavelength. We show that this upconversion process causes strong quenching of the lasing power at 3.4 μm under insufficient 974 nm pumping. Intracavity fluorescence at 550 nm from levels (
²
H
_11/2
,
⁴
S
_3/2
) is also monitored as a witness of this excited state absorption mechanism. Through numerical modeling, we estimate the cross section value of the process and show that it is essential to reproduce both power and fluorescence curves. This paper also emphasizes the critical role played by the pump wavelengths.