Critical density effects in sub-picosecond laser-ablation of silicon by plasma absorption ion-energy spectroscopy

Summary form only given. This paper discusses the efficiency of absorption of sub-picosecond laser pulses during the formation of ablation plasma plumes from a silicon solid target. Such plasmas are normally used to fabricate thin films on a heated substrate. Properties of the plasma such as temperature, density energy, and species can affect growth mechanisms and the final film quality. The energy and the associated flux density in ablation plasmas are a function of the percentage of energy extracted from the incoming laser pulse at the target. It is shown in this work that the critical density condition of a plasma initially formed by a single pulse can be subsequently modified by the pumping action of a secondary time-delayed pulse.