A research group led by Prof. FU Yuxi from Xi'an Institute of Optics and Precision Mechanics (XIOPM) of the Chinese Academy of Sciences developed the world's first room temperature holmium-doped yttrium lithium fluoride (Ho: YLF) composite thin disk laser, which can achieve high efficiency and quality continuous-wave laser output. This research has overcome the technical limitation of 2 μm lasers relying on low-temperature cooling, offering a novel approach for developing high-power and portable infrared laser systems.
The research results were published in Optics Express.
Lasers operating in the 2 µm spectral range are highly valued for their eye safety, high water absorption, and low atmospheric attenuation, which make them crucial in diverse applications. Nevertheless, conventional 2 µm lasers typically require cryogenic cooling to control thermal effects, which increases system complexity and cost and restricts their use in compact, space-constrained, and mobile platforms. Consequently, developing high-power, room-temperature 2 µm lasers has become a pivotal research area.
In this study, a novel composite thin-disk structure based on Ho: YLF was developed. By bonding a 2 at. % doped Ho: YLF crystal with an undoped YLF cap layer, the mechanical robustness of the crystal was significantly improved, while the amplified spontaneous emission effects were effectively suppressed, leading to enhanced laser output stability. Furthermore, researchers optimized the optical pumping system by implementing a multi-pass configuration with 12 pump cycles, combined with an efficient thermal management strategy. This approach not only ensured high-power output but also minimized thermal lensing effects, resulting in superior beam quality.
Experimental results show that when the laser is pumped by a 1940 nm Tm-doped fiber laser with a 1.8 mm diameter pump spot, it reaches a peak output power of 26.5 W, the optical efficiency is 38.1% and the slope efficiency is 42.0%. Moreover, the beam quality is nearly at the diffraction limit, and the relative standard deviation of power stability is only 0.35%.
“This work paves the way for compact, cost-effective high-power 2 µm lasers, with the potential to scale to the 100 W level and drive advancements in ultrafast laser science,” said Prof. FU Yuxi from XIOPM.
(Published 13 February 2025)
Fig. Schematic of the Ho: YLF thin-disk laser. (a) Three-dimensional schematic of the thin-disk laser based on the 12-pass pumping module. (b) Diagram of the experimental setup, showing a composite thin disk laser head with a water-cooled heat sink. (Image by XIOPM)
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