Laserline (Germany)

In this paper, we report on a novel measurement setup for emitter resolved characterization of polarization, optical output power, wavelength, and slow-axis intensity distribution of high-power diode laser bars. Our setup enables the emitter-resolved characterization in a range starting from below the laser threshold reaching up to several 100 amps correlating to operating power of the state-of-the-art generation of diode laser bars, which possess a power output of several 100 watts. In contrast to previous works, the properties are determined directly from the laser radiation during operation, which enables us to directly correlate the emitter-resolved power and polarization distribution. In addition to the reduction in degree of polarization towards the edge emitters, we demonstrate a disparity in power distribution among the edge emitters at operating output power in comparison to operation below the laser threshold. To distinguish between thermal and stress-induced effects, we operate the diode laser bar both in cw- and pulsed mode. Furthermore, we demonstrate how the effects of mechanical stress on the performance and degree of polarization of the edge emitters at operating power are identified.

In the recent years, laser beam welding has become an established joining process, especially for components in the electrical powertrain (copper applications). However, laser beam welding of copper is generally considered to be difficult, particularly due to its high heat conductivity and due to its low absorptivity using laser sources with a wavelength of 1 μm. The resulting welds show numerous weld defects, such as pores and spatters. Using “blue” lasers with a wavelength of 450 nm promises a smoother welding process with less spatters. Therefore, a blue diode laser with increased absorptivity in copper materials was developed by Laserline and used for welding copper. In this contribution, the results of welding copper using blue lasers with respect to the penetration depth and the resulting weld quality are discussed. In addition, investigations by Bosch at the electron-synchrotron DESY with a blue diode laser enabled us to have a look into the material during welding. Consequently, melt pool dynamics and capillary dynamics were analyzed with respect to the formation of weld defects and will be discussed as well. Furthermore, it is demonstrated that it can be beneficial to use a so-called spot-in-spot beam shaping tool to further improve the melt pool dynamics and, therefore, the resulting weld quality.

In this paper, we present our current work towards a highly efficient XLMA (extra-large mode area) fiber-based laser, which is being performed in the EKOLAS consortium within the BMBF-funded EffiLAS (efficient high-performance laser beam sources) research alliance. To this end, the complete manufacturing process chain of the XLMA fiber was reviewed and optimized. The work started with the material composition of the active XLMA preform with the goal of improving the purity and thus the background loss. A successfully implemented fluorine co-doping process allows refractive index adjustment of the active core material which improves the beam quality of the laser fibers without changing the concentration of active ions in the glass composition. The preform is subjected to a screening in which possible scatter centers, e.g. bubbles, inclusions or contaminants, are mapped and categorized, in order to identify defects, which could lead to a failure in the drawn fiber, already at an early production stage. The subsequent fiber drawing is monitored for scattering using the emissions from the heated preform as well as for inhomogeneities of the dopants using a phase measurement technique. Finally, the fiber is tested for residual impurities and background losses using a multi-mode OTDR to ensure that the fibers are free of any defects.

Today, high performance components rely on a controlled heat dissipation by copper layers, which can be applied by laser cladding with lasers in the near-infrared (NIR) wavelength. However, current cladding processes are restricted to copper alloys with reduced heat conduction in order to achieve a sufficient melting of the material. The challenge of pure copper is the high reflectivity in the NIR wavelength range and the variation of the heat dissipation during the melting of the copper material. This leads conventionally to an undefined energy coupling into the substrate and process instabilities, which can cause a variation in the melting depth and pores in the layers. With the application of a laser wavelength of 450nm, the laser absorption in pure copper is highly improved and similar to alloyed copper or even steel, which allows for a reproducible melting even of pure copper material. This processing opportunity is enabled for the first time with the development of a novel high power blue laser source with 1kW output power at 450 nm wavelength in continuous wave mode, which is applied for the cladding of pure copper powder. In this contribution we will demonstrate the performance of a high power blue laser cladding process of pure copper powder on steel and on copper substrate. The assessment of the resulting homogeneity and reproducibility of the resulting copper coatings give new perspectives for conventional applications such as heat pipes or heat dissipation layers but also for new applications such as pure copper components produced by additive manufacturing.

XLMA fibers based on Yb-doped bulk silica possess an excellent refractive index and doping level homogeneity [1]. To achieve the highest optical-to-optical efficiency and long-term operation without degradation we simulated the effect of the brightness conversion factor of different core dopant compositions of such XLMA fibers. We also investigated the beam quality of a multi-kW single XLMA fiber laser system and its long-term stability. The current state-of-the-art XLMA single fiber laser has 5 kW maximum output power and a degradation rate of about 0.5 % / 500 h at 4 kW measured over a period of 1700 h. Several application tests demonstrate the excellent performance of the XLMA fiber laser.