- Text Size:
The Laser User Magazine
Issue 059 - Summer 2010
The influence of laser-induced focus shift on high power fibre laser welding
Author: Daniel Reitemeyer, Thomas Seefeld, Frank Vollertsen and Jean Pierre Bergmann
State of the art multimode thin disc and fibre lasers offer a combination of high output power and high beam quality. The beam of these diode pumped solid state lasers is delivered by optical fibre and for material processing applications the fibre delivers the laser output to a processing head, where it is focused onto the workpiece. However, at laser power levels of around 1 kW and above laserinduced focus shift has been observed, which can have a deleterious effect on the quality of the materials processing. This paper Investigates the laser power and time dependence of the phenomenon and its effect on laser welding.
A sketch of the optical set-up shows a typical welding head, which is also the arrangement used for this study. Essentially, the divergent laser output of the fibre is made parallel by a collimation unit and is then focused, producing an image of the fibre end in the
focal plane, which is set on or abut the workpiece surface.
The combination of high laser power and high beam quality causes significant thermal loading of optical elements and changes in their shape and optical properties. The leads to changes in beam geometry that in turn .........