High-brightness high-power kW system with tapered diode laser bars

We report on a diode laser system, which is based on tapered diode laser bars and provides a combination of high power and high beam quality comparable to high power lamp pumped solid-state-rod lasers. Until now diode laser systems with output powers in the kW-range are based on broad area diode lasers. However, the output of these kilowatt laser systems usually is characterized by a strongly asymmetric beam profile, which is a consequence of the asymmetric beam parameter product (BPP) of broad area diode lasers with regard to the slow- and the fast-axis direction. Apparently the output of such a laser system can not be coupled efficiently into a fiber, which is required for a variety of applications. The symmetrization of the BPP of such a laser system requires complicated and expensive beam shaping systems. In contrast tapered diode laser bars allow the design of high power laser systems with a symmetric beam profile without the necessity of using sophisticated beam shaping systems. Power scaling is realized with different incoherent coupling principles, including spatial multiplexing, polarization multiplexing and wavelength multiplexing. The total output power of the tapered diode laser system was 3230 W at a current of 75 A. Fiber coupling yielded 2380 W at 75 A for a fiber with a core diameter of 800 μm (NA 0.22) and 1650 W at 60 A for a 600 μm fiber (NA 0.22), respectively. Focusing with an objective with a focal length of 62 mm led to a beam diameter of 0.52 mm in the focal plane. Taking into account the total power of 2380 W behind the fiber the resulting intensity in the focal plane was 1.1 MW/cm 2 .