High-power fiber lasers have become one of the most important tools for material processing in the last decade. Laserline GmbH, which is primarily known for its multi-kilowatt direct-diode lasers, also introduced a fiber-laser platform as a brightness converter for its direct-diode lasers a few years ago. Currently, output powers up to 6 kW at beam qualities down to 4 mm mrad are commercially available. The platform is based on a single directly water-cooled ytterbium doped XLMA (extra-large mode area) fiber in an end-pumped configuration, which can easily be combined in series with a standard diode laser. In this paper, we present the latest progress in power scaling of our fiber-laser system. By improving the material properties of the active fiber, the thermal management and the thermo-mechanical stability of the resonator, up to 10 kW output power from a single, unidirectionally pumped fiber-laser oscillator with a beam parameter product in the range of 4 mm mrad to 8 mm mrad is demonstrated. Further power scaling up to 17.5 kW with 8 mm mrad was achieved by bidirectional pumping of the active fiber. In both cases, a rather high optical conversion efficiency of 75-77 % leads to a wall-plug efficiency of ~35 % for the whole laser system. Currently, we do not observe any physical limits, such as nonlinear effects for example.
The disk laser is one of the most important laser concepts for today’s industrial laser market. Offering high brilliance at low cost, high optical efficiency and great application flexibility the disk laser paved the way for many industrial laser applications. Over the past years power and brightness increased and the disk laser turned out to be a very versatile laser source, not only for welding but also for cutting. Both, the quality and speed of cutting are superior to CO<sub>2</sub>-based lasers for a vast majority of metals, and, most important, in a broad thickness range. In addition, due to the insensitivity against back reflections the disk laser is well suited for cutting highly reflective metal such as brass or copper. These advantages facilitate versatile cutting machines and explain the high and growing demand for disk lasers for applications besides welding applications that can be observed today. From a today’s perspective the disk principle has not reached any fundamental limits regarding output power per disk or beam quality, and offers numerous advantages over other high power resonator concepts, especially over fiber lasers or direct diode lasers. This paper will give insight in the latest progress in kilowatt class cw disk laser technology at TRUMPF and will discuss recent power scaling results as well.