New Components The Two-Micrometer Laser is Now Becoming More Powerful

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The experts from the Laser Center Hannover (Germany) (LZH) say that lasers with a wavelength of two micrometers excel in medical technology and plastics engineering. Now there's a breakthrough ...

Fiber lasers doped with the element thulium operate at a wavelength of around two micrometers and are therefore particularly suitable for applications where conventional lasers reach their limits, explain the experts from LZH. However, until now, there has been a lack of commercially available laser sources that simultaneously offer high beam quality, sufficient laser power, and reliable operation in the so-called "quasi continuous wave" mode at power levels around one kilowatt, as further stated. The Eurostars project Decomp aims to achieve this. According to reports, scientists at LZH are developing novel fiber optic components based on so-called "triple clad" fibers, which enable the construction of a reliable and low-maintenance laser architecture. To implement the final laser system, LZH collaborated with Futonics Laser as well as the South Korean partners Coset Inc. and the Korean Photonics Technology Institute. For this purpose, the LZH team used an innovative, self-developed, and patented processing technique based on the CO2 laser principle, as emphasized.

High Coupling Efficiency with only 475 watts of Input Power

With this, the researchers specifically removed small areas of the outermost glass cladding of the TC fibers, thereby creating a lateral access to the pump cladding. This technique enables the fibers of the pump diodes to be fused laterally to the pump light cladding, i.e., the inner glass cladding. This makes the required pump energy available for the laser process, it is stated. Additionally, so-called cladding mode strippers were developed in Hanover, which efficiently remove unabsorbed pump light from the fiber system through CO2 laser structuring of the TC fiber. The developed signal-pump couplers then achieved an average coupling efficiency of 90.1 percent (±2.5 percent)—at input powers of up to 475 watts. However, the process was limited by the available pump power. Nevertheless, this achieved an efficiency that corresponds to the state of the art of couplers with conventional fibers. For TC fibers, this is an impressive innovation. And the relatively low optical losses suggest that the component can also be operated at significantly higher powers.

The "Triple-Clad" Fiber Design Becomes Usable for Various Laser Setups

This makes it possible to achieve the targeted 1-kilowatt power class in lasers. The scientists from Hanover (Germany) ultimately achieved an extraction efficiency of over 20 decibels with the cladding mode strippers, with a derived optical power of 250 watts. These components thus make the "triple clad" fiber design usable for various laser and amplifier setups. They enable higher fiber integration as well as further power scaling in systems with demanding beam quality requirements, as noted by the LZH experts. The project "Development of high-performance QCW 2µm fiber lasers for medical and agricultural applications" (Decomp) was supported under the Eurostars program with funding reference numbers E!234 and 01QE2206B.