Product Code: ICAL07_202

Focusing of High Power Single Mode Laser Beams
Authors:
Axel Hess, Forschungsgesellschaft für Strahlwerkzeuge mbH (FGSW); Stuttgart Germany
Felix Abt, Forschungsgesellschaft F�R Strahlwerkzeuge Mbh (FGSW); Stuttgart Germany
Friedrich Dausinger, Forschungsgesellschaft F�R Strahlwerkzeuge Mbh (FGSW); Stuttgart Germany
Presented at ICALEO 2007

Newest developments in diode pumped solid state lasers brought up thin disk- and fibre lasers with beam qualities in the range of M² = 10 to M² = 1 at an output power of up to 2 kW. To achieve the appropriate power density distribu-tion for material processing, the laser beam has to be transformed by a lens system. When using laser beams of strong focusability, a degradation of the beam quality becomes an important issue. Due to imperfections of the involved lenses, the M² might be worse than expected. So the focus diameter might be larger as calculated. The laser induced focal shift is mainly caused by the radial gradient of the refraction index, due to absorbed laser light. This process is strongly dependent on the power density of the laser beam and the cool-ing of the optical components.
Sophisticated measurement of the beam quality degradation and the focal shift revealed that the high beam qualities are increasing the require-ments on the optical system of laser processing heads. Many of todays standard optics do not meet these demands. The solution of these prob-lems will be a key factor for the industrial usabil-ity of high brilliant lasers.