New Components The Two-Micrometer Laser is Now More Powerful

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The experts at the Laser-Zentrum in Germany, Hannover (LZH) say that lasers with a wavelength of two micrometers score highly in medical technology and plastics technology, for example. 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 at the LZH. Until now, however, there has been a lack of commercially available laser sources that simultaneously offer high beam quality, sufficient laser power and also work reliably in so-called "quasi-continuous wave" operation at power levels of around one kilowatt, they continue. The Eurostars project Decomp aims to achieve this. Scientists at the LZH are developing innovative fiber optic components based on so-called "triple clad" fibers, which can be used to build a reliable and low-maintenance laser architecture. To implement the final laser system, the LZH worked together with Futonics Laser and its South Korean partners Coset Inc. and the Korean Photonics Technology Institute. As emphasized, the LZH team used an innovative, self-developed and patented processing technology based on the CO₂ laser principle.

High Coupling Efficiency With Only 475 Watts Input Power

The researchers used this to remove small areas of the outermost glass cladding of the TC fibers in a targeted manner, thus creating lateral access to the pump cladding. This technique makes it possible to melt the fibers of the pump diodes to the side of the pump cladding, i.e. the inner glass cladding. This means that the required pump energy can be made available for the laser process, they say. In addition, so-called cladding mode strippers were developed in Hanover, which efficiently remove unabsorbed pump light from the fiber system by means of 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)—with a maximum input power of 475 watts. However, the available pump power limited the process. Nevertheless, an efficiency was achieved that corresponds to the state of the art of couplers with conventional fibers. This is an impressive first for TC fibers. And the relatively low optical losses indicate that the component can also be operated at significantly higher power levels.

The "Triple Clad" Fiber Design Can Be Used for Various Laser Setups

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

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