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Researchers develop first room temperature holmium-doped yttrium lithium fluoride thin disk laser

In a study in Optics Express, a research group led by Prof. Fu Yuxi from Xi'an Institute of Optics and Precision Mechanics (XIOPM) of the Chinese Academy of Sciences has developed the 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.

Lasers operating in the 2 µm spectral range are highly valued for their eye safety, high water absorption, and low atmospheric attenuation.

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. Therefore, developing high-power, room-temperature 2 µm lasers has become a vital research direction.

In this study, researchers developed a novel composite thin-disk structure based on Ho:YLF. Through 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 showed that when the laser was pumped by a 1,940 nm Tm-doped fiber laser with a 1.8 mm diameter pump spot, it reached a peak output power of 26.5 W with optical efficiency being 38.1% and the slope efficiency being 42.0%. The beam quality was nearly at the diffraction limit, and the relative standard deviation of power stability was 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. It also offers a novel approach for developing high-power and portable infrared laser systems," said Prof. Fu.