Electron and ion emission characteristics of metal irradiated by nanosecond laser

Abstract

Clarifying the electron and ion emission characteristics of metals irradiated by nanosecond focused laser in low pressure environment is crucial for improving applications based on laser-produced plasmas (LPPs). This paper investigates the emission characteristics through electrical and optical diagnosis. The emission process is investigated through joint analysis of electrons and ions behavior, and relevant influencing factors are studied. The emission process of electrons and ions is divided into four stages, characterized by the arrival of prompt electrons e1, ultrafast electrons e2/ions i1, fast ions i2 and thermal electrons e3/ions i3, respectively. e1 is mainly related to thermal emission and photoemission, which can be improved by high electric field, gas pressure (within a certain range), laser energy and melting boiling points of target. e2/e3 and i1/i2/i3 mainly originate from laser ablation, and their expansion process follows obvious bipolar diffusion characteristics, while the latter is related to the different mass and charge states of the ions. The amplitude of i2 and e3 can be improved by using low density and melting point metals, and they are easily blocked by background gas, almost independent of the weak electric field.