Experimental and first principles assessment of plasma attenuation during laser treatment of an Al alloy

Abstract

The effect of single-pulse plasma attenuation on a KrF excimer laser beam during irradiation of an Al 6061 alloy in ambient conditions was studied. The lowest attenuation was experimentally observed for a laser power density of 200 MW cm−2 per pulse, based on the material’s surface roughness; the latter energy was determined as the critical point of the transition from an initial attenuation mode to the final one in a doubled stepped mechanism. Using a combination of profilometry and density functional theory, the second (high-energy) mode was determined as owing to a combination of plasma detachment and increased melt flow due to peak cavitation into the troughs created by the laser. The effect of energy absorption by the material’s surface was modelled as the energy required to remove three crystal layers along the [001] direction of a pure Al alloy with a unit cell constant of 4·050 Å.