Charging and plasma effects under ultrashort pulsed laser ablation

Based on experiments and a theoretical analysis, we raise questions on two fundamental mechanisms of femtosecond laser desorption/ablation of solids, namely Coulomb explosion (CE) and plasma etching. The effects of laser-induced ionization and surface charging are analyzed which can be responsible for ultrafast ions observed in time-of-flight mass-spectra under ultrashort laser irradiation of solids. The importance of surface charging in formation of velocity distributions of desorbed/ablated species has been revealed for conditions when the CE mechanism is inhibited. The influence of ambient plasma formation on the dynamics of heating of metallic targets by femtosecond laser pulses is studied based on 2D modeling of laser-induced target heating and dynamics of the ambient plasma. The calculations show an intriguing picture of the laser-induced ambient gas motion. We propose a model of laser-induced breakdown of an ambient gas in a region in front of the irradiated target and analyze plasma-chemical processes which can affect laser processing of surfaces in the presence of air or highly reactive media.