Experimental and theoretical comparison of ion properties from nanosecond laser-produced plasmas of metal targets

Abstract

The ion emission properties of laser-produced plasmas as a function of laser intensities between 4–50 GW cm−2 and varying angles with respect to the target normal were investigated. The plasmas were produced by focusing 1064 nm, 6 ns pulses from an Nd:YAG laser on various metal targets. The targets used for this study include Ti, Mo, and Gd (Z=22,42,64). It is noted that all ion profiles are composed of multiple peaks—a prompt emission peak trailed by three ion peaks (ultrafast, fast, and thermal). Experimentally, it is shown that each of these ion peaks follows a unique trend as a function of laser intensity, angle, and distance away from the target. Theoretically, it is shown that simple analytical models can be used to explain the properties of the ions. The variations in the ion velocity and density as a function of laser intensity are found to be in good agreement with theoretical models of sheath acceleration, isothermal self-similar expansion, and ablative plasma flow for various ion peaks.

Electron and ion emission characteristics of metal irradiated by nanosecond laser

“…This voltage can distinguish between electron and ion emission processes while minimizing the impact of external electric field on LPPs. It can be seen that the emission process is divided into four stages, similar to Polek's research results [19]. Meanwhile, there are also differences between Mg with low melting point and Cu with high melting point.…”

“…When U < 0, it can be seen that the amplitude of the prompt electrons e 1 decreases continuously with the voltage due to the repulsion of the Faraday cup, and eventually forms the prompt ions peak, which is related to the collision ionization of the prompt electrons near the Faraday cup, or the photoionization of the gas nearby by the strong ultraviolet light emitted by initial LPPs [19]. On the contrary, different weak voltages have a relatively small impact on the diffusion process of i 1 and i 2 .…”

“…The emitted ions mainly come from metal vapor with high temperature and pressure, as well as gas pushed by them. Polek has provided a complete description of the TOF waveform of ions from LPPs [19], showing four peaks corresponding to prompt ions, ultrafast ions, fast ions and thermal ions respectively. Some related physical mechanisms have also been described.…”

Study of atoms and multiply charged ions features in the nanosecond laser produced Mo plasma in vacuum using optical emission spectroscopy and time-of-flight electrostatic energy analyzer

“…Figure 7(a) gives the temporal profiles of the charge-state resolved Mo n+ (n = 1-5). The temporal profiles are obtained by scanning the KE/Z from 0 to 1000 V with a step of 5 V. In many investigations, Faraday cup has been used to investigate the temporal evolution of ions during the expansion, while the signal is not charge-state resolved [27,[58][59][60]. The charge-state resolved temporal profiles of Mo n+ provides important information for the theoretic models to explain the properties of the ions.…”

“…Moreover, the extremely condition in tokamak like vacuum, strong magnetic field, discharge plasma background made the LIBS quantitative analysis further complicated. The basic processes of nanosecond laser ablation with subsequent plasma formation and expansion have been investigated in depth in recent years using theoretical simulations [15][16][17][18][19][20][21][22] and experimental methods [23][24][25][26][27], which also have been summarized in detail in numerous investigations and books [9,26,[28][29][30][31][32]. Nevertheless, the long-time scale and space dependent properties make the full description of laser ablation and plasma formation still challenging.…”