Dynamic and absolute measurements of laser coupling efficiency during laser spot welds

Laser absorptance (coupling efficiency) changes rapidly during laser metal processing due to temperature and multiple phase changes. We find that there is limited literature data available, but that this property is vital for accurate process simulations, as well as the fundamental understanding of the dynamics of high-power laser-matter interaction. We measure the dynamic, absolute absorbed power with sub-microsecond resolution during a 10 ms laser spot weld in 316L stainless steel from conduction to keyhole welding conditions using an integrating sphere. Our data show several important features including the points of melting and keyhole formation. Conclusions from the optical data are supported by weld cross-section analysis.