Optical spectral analysis of the laser weld plume is common practice as it is a non-contact, in situ technique. However, the low sensitivity of optical emission spectroscopy limits the available information during 1070 nm wavelength laser welding, which is becoming the standard in many industrial operations. Here we demonstrate dramatically improved sensitivity of optical spectroscopy by applying laser-induced fluorescence (LIF) for probing the hot gas plume induced during fiber laser welding of 304L stainless steel. As a proof-of-principle, we show that LIF is capable of resolving a spectral signal from silicon being emitted during welding. Optical detection of such a low concentration alloying element has not previously been reported and shows the capability of LIF for increased sensitivity. Silicon atoms in the weld plume were excited in the ultraviolet at 221.09 nm and detected at 221.64 nm. We demonstrate the detection of silicon LIF down to laser welding powers of 603.4 W (213 kW/cm2) making this technique applicable even in low-power laser welding or additive manufacturing scenarios.
Journal of Physics D-Applied Physics