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

Abstract

Dynamics of the plume produced due to the interaction of millisecond infrared fiber lasers having different spectral profiles with titanium is investigated by high-speed imaging (HSI) and optical emission spectroscopy (OES) at different ambient atmospheres and pressures. The surface quality is associated with different plume dynamics that depends on the processing conditions. Reabsorption of the laser pulse by the neutral titanium atoms due to overlap of laser spectral profile with corresponding transition energies causes deposition of nanoparticles on the surface around the spot produced by the laser, which results in surface contamination and darkness around the spot. Increasing confinement of plume in Ar ambient than Ar/He leads to more darkness around the spot due to more availability of Ti species in a smaller volume for reabsorption. In vacuum/at low pressures, larger size of the expanding plume causes a smaller number of Ti species to interact with the laser pulse that produces clean surface around the spot. The surface contamination is prevented irrespective of the processing conditions by using the laser with customized spectral profile, which does not overlap with any neutral titanium atomic transitions (Ti I).