Product Code: ICAL08_1302

Temporal Behaviour of the Focal Shift of Beam Forming Optics for High Power Single Mode Lasers
Authors:
Axel Hess, Forschungsgesellschaft fuer Strahlwerkzeuge FGSW; Stuttgart Germany
Felix Abt, Forschungsgesellschaft fuer Strahlwerkzeuge FGSW; Stuttgart Germany
Friedrich Dausinger, Forschungsgesellschaft fuer Strahlwerkzeuge FGSW; Stuttgart Germany
Presented at ICALEO 2008

New generations of thin disk and fibre lasers are combining excellent beam quality typically having M² between 1.2 and approximately 8 with kilowatts of output power. This combination of power and beam quality brings the imaging performance of beam-forming optics into focus. Former research on the beam quality degradation and the focal shift revealed that the high beam qualities are increasing the requirements on the optical system of laser processing heads. In many cases the degradation in beam quality and the focal shift inhibits stable process conditions. Furthermore the classical calculation of the spot size on the work piece doesnt work for high power diffraction limited lasers. To pre-estimate the impact of the laser induced focal shift on a specific process, one has to know the temporal response of an optical system to a change of the used laser power. Therefore the step function response of the laser induced focal shift of beam forming optics was measured with high temporal resolution. These sophisticated measurements in different time scales of a wide range of beam forming optics brought up a comprehensive basis to estimate the impact of the laser induced focal shift on specific laser based processes.