Mid-infrared lasers operating in the 3–5 μm region are of interest for spectroscopy and atmosphere sensing applications. Although the 4F9/2→4I9/2 transition in Er-doped fluoride fiber enables efficient 3.5 μm laser emission, power scaling remains challenging due to significant laser quenching effects and limited power handling capability of fluoride fibers. In this work, we demonstrate a high-power 3.5 μm Er-doped fluoride fiber laser with a spatial cavity configuration. Numerical modeling is performed to analyze the power and thermal behavior of the laser to determine an optimized routine for efficient power amplification with low thermal load, based on which a maximum output power reaching 16.4 W at 3.46 μm was experimentally demonstrated. Significant wavelength redshift with the increase of 2 μm pump power is observed under insufficient 0.98 μm pump power due to reduced population inversion, which offers a straightforward method for wavelength tuning in a broadband-feedback cavity.
Zhang et al. (Sun,) studied this question.