Saturation effects in the laser ablation of stainless steel in air at atmospheric pressure

A pulsed Nd:YAG laser was used to generate a plasma from stainless steel ta rgets in air at atmospheric pressure. Laser focusing was found to be an imp ortant factor in the ablation process. The influence of focal conditions on spatial profiles of plasma, emission intensity and averaged ablation rate (AAR, mu m pulse(-1)) of stainless steel samples as a function of laser ene rgy are discussed. At high energies and depending on laser beam focusing, a blation efficiency tends to decrease compared to that at lower energies. Th is effect can be due to plasma shielding and air breakdown. The averaged ab lation rate was found to be dependent on the thickness of the sample. This effect results in shielding of the incoming laser beam and redeposition of removed material in the crater. By focusing the beam inside the material fr ee expansion of plasma is allowed, resulting in more efficient erosion of t he sample at larger energies. For comparative purposes, data on ablated mas s per pulse are presented.