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19 Feb 2025
Research team from the Chinese Academy of Sciences develops thin-disk source based around Ho:YLF crystal.
Researchers in China have published details of a new holmium-doped laser emitting at a wavelength close to 2 µm that they claim could pave the way to a new class of compact and cost-effective sources for medical and materials processing applications.
Detailed in a paper just published in the journal Optics Express, the experimental setup uses a tellurium-doped fiber laser operating at 1940 nm to pump a thin-disk holmium-doped yttrium lithium fluoride (Ho:YLF) crystal.
Yuxi Fu and colleagues, who work at the Xi'an Institute of Optics and Precision Mechanics, reported a continuous-wave, near-diffraction-limited output reaching a maximum of 26.5 Watts at around 2060 nm.
“To the best of our knowledge, this is the first report of a Ho:YLF composite thin disk laser at room temperature,” they wrote.
Composite disk
According to a Chinese Academy of Sciences release detailing the research, lasers operating in the 2 µm spectral range are highly valued for their eye safety, high water absorption, and low atmospheric attenuation.
However, it points out that conventional 2 µm lasers typically require cryogenic cooling to control thermal effects, increasing system complexity and cost. As a result, current high-power designs are not suitable for use in compact, space-constrained, or mobile platforms.
The reported thin-disk structure is a composite design, comprising an a-cut Ho:YLF laser crystal measuring 8 mm × 8 mm × 0.5 mm with 2 per cent holmium-ion doping concentration that was bonded to an undoped YLF cap layer to ensure mechanical robustness.
The rear surface of the composite disk was coated with a high-reflectivity layer effective at 1900-2100 nm, covering both the pump wavelength and the emission band. And instead of a cryogenic cooling system, the design incorporated a water-cooled silicon carbide heat sink.
“Further efforts are required to scale up the output power, which can be achieved by optimizing the doping concentration and thickness of the crystals, increasing the number of pump passes, enhancing heat dissipation strategies, and further increasing the pump power,” concluded the team in its paper.
“Future investigations are also needed to explore the performance of Ho:YLF composite thin-disk amplifiers.”
Femtosecond potential
While at an early stage, the results highlight the potential of thin-disk Ho:YLF lasers as a route to efficient and compact 2 µm sources, with potential applications in precision material processing, laser surgery, and remote sensing.
The team also suggests that the broad emission bandwidth of the Ho:YLF crystal may present an opportunity to generate terawatt-class femtosecond pulses around the 2 µm wavelength.
That capability could even lead to applications in high-flux attosecond pulse production in the soft X-ray regime, they reported, before concluding:
“The presented Ho:YLF composite thin-disk laser can be considered as a proof-of-concept for the further development of high-power 2 μm laser system[s].”
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