The widespread applications of lasers operating at wavelengths of approximately 2 μm span across various fields, including medicine, communication, and the environment. Co-affected by the multiphoton absorption effects and residual hydroxyl group absorption, the highest laser output efficiency of Ho3+-doped silica fiber at 2 μm is capped at 87%.
Using infrared glass fiber is an effective way to further improve the laser output efficiency. Fluorotellurite glass fiber is a promising alternative material, which has advantages such as low phonon energy, high laser damage threshold, high rare earth solubility, and good chemical stability compared to other infrared glasses. However, the development of fluorotellurite glass fiber is still immature, and its high fiber loss and easy damage under high power laser pumping limit its 2 μm laser output performance.
A research team led by Prof. Dr. GUO Haitao from Xi'an Institute of Optics and Precision Mechanics (XIOPM) of the Chinese Academy of Sciences (CAS) achieved a longwave output at 2085 nm with a slope efficiency of ~ 90.4 % and unsaturated maximum output power of 6.35 W in a Ho3+-doped fluorotellurite glass fiber pumped by a homemade 1976 nm fiber laser. The result was published in Optics and Laser Technology.
The performance of fiber directly affects the output of fiber laser. Fluorotellurite glass fiber with a low loss of 0.59 dB/m at 1550 nm and a good laser damage resistance ability was used in this study.
(a) The output spectrum of the 2085 nm laser. The inset: output spectrum of the unseparated laser. (b) The slope efficiency of the 2085 nm laser output. (Image by XIOPM)
By spatial 1976 nm laser pumping, a 2085 nm laser output form a 25 cm long fluorotellurite glass fiber was achieved with a high slop efficiency of 90.4% and an unsaturated maximum output power of 6.35 W. The full width at half-maximum of the excitation line was measured to be 3.1 nm. Researchers believed that a laser output power scale-up of over 10 W can be achieved after further optimization of the device.
This work offers valuable insights for the future development of high-efficient, long-wavelength mid-infrared ~ 2.1 μm fiber lasers.
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