Time-Resolved Detection of Vaporization during Laser Metal Processing with Laser-induced Fluorescence

Abstract Element loss during high-power laser processing of metals can lead to deleterious chemical and mechanical effects that negatively impact the processed material’s quality. Currently, there is no suitable way to measure time-resolved element loss in situ during laser processing. In this work, we show that laser-induced fluorescence (LIF) can be used to temporally resolve individual element vaporization during a laser spot welding of 316L stainless steel. As a proof-of-concept, we measured iron loss during a 500 µs laser spot weld with a time resolution of 5 microseconds. We found that keyhole formation could clearly be identified by a dramatic increase in iron emission from the weld pool. This conclusion was validated by independent, time-resolved measurements of laser absorptance during laser spot welding from our previous work.