Effect of plume dynamics on surface contamination during interaction of millisecond infrared fiber laser with titanium

•Influence of plume dynamics on surface contamination during interaction of laser with titanium investigated by high-speed imaging and optical emission spectroscopy.•Reabsorption of the laser pulse by neutral titanium atoms in the plume results in dark colouration around the laser spot on the weld surface.•Effect of ambient gas atmospheres, pressures, laser's spectral profiles, powers and pulse durations on plume dynamics and surface contamination.•Clean weld appearance for laser with customized spectral profile, which does not overlap with neutral atomic titanium transitions.