Diagnosis of electron temperature and density in the early stage of laser-produced Si plasma expansion

Abstract

We measured time-resolved spectra of laser-produced plasma of Si in a vacuum at the early phase evolution (30–100 ns) and found clear signs of spectral line broadening. Based on the measured line intensities of Si2+ and Si3+ ions, the Saha–Boltzmann method is used to diagnose the electron temperature. The Stark broadening of different high-charge ion lines is combined with a modified Griem semi-empirical formula to diagnose the electron density of Si plasma in the early evolutionary stage. The effects of self-absorption, natural broadening, and Doppler broadening on the spectral profiles were evaluated. We also conducted experiments to verify that current experimental conditions satisfied the local thermodynamic equilibrium conditions. Finally, time evolutions for the electron temperature and electron density in the early stage of plasma evolution were obtained.

Electron impact cross-sections and rate coefficients of Si+2 ions relevant to collisional radiative modeling of silicon plasma

“…We find that Wang et al [19] have performed OES measurements on early-stage (30-100 ns) expansion of laser-produced silicon plasma and recorded the line emissions from Si +2 and Si +3 ionic states at short time delays of 5 ns. The plasma was generated on the planar surface of silicon placed in vacuum using a 1064 nm Nd:YAG laser (PRO-350, Spectra-Physics) with 10 ns pulse width and laser power density of 2.04 × 10 11 W cm −2 .…”

“…For example, laser-ablated silicon plasma has been applied for pulse laser deposition, etching processes, etc [15][16][17]. Considering these applications, a few efforts have been made for the diagnostic of silicon plasma [18,19]. However, in most of the work, the local thermodynamic equilibrium (LTE) [20] condition has been assumed for the characterization of the plasma.…”

“…However, in most of the work, the local thermodynamic equilibrium (LTE) [20] condition has been assumed for the characterization of the plasma. Recently, Wang et al [19] have performed the optical diagnostic of early-stage expansion of laser-produced silicon plasma in which they have estimated the electron density using Stark broadening and the electron temperature using the Boltzmann plot method. The Boltzmann plot method is based on the LTE assumption of the plasma and the excitation temperature of the emitting species is considered equal to the electron temperature.…”

Numerical simulation of nanosecond laser ablation and plasma characteristics considering a real gas equation of state

“…In addition, the applicability of the real gas approximation also needs to be verified by experimental results. In our previous work [32], we measured the temperature and electron density of Si plasma using time-resolved spectra, and obtained a plasma temperature of 2.75 eV at 30 ns. It can be seen from figure 8 that the plasma temperature calculated by the real gas approximation is 2.71 eV at 30 ns and most consistent with the experimental result.…”

Research on plasma electron density distribution based on microwave diffraction

“…Generally, the plasma parameter diagnosis methods include the Langmuir probe method [6][7][8][9], laser interferometry [10][11][12], spectroscopy diagnosis method [13,14], microwave diagnosis method [15][16][17][18][19], and so on. Each method has a certain scope of application and limitations.…”