Influences of Partition Function Cutoff Versus Lowering of Ionization Energy on Spectroscopic Temperature Measurement in Aluminum Plasmas

Spectral diagnosis is the primary approach to understanding the properties and behaviors of thermal plasmas. The partition function cutoff and the lowering of ionization energy directly influence the results of spectral radiation calculation. To investigate the effects of two factors on spectral analysis, this study uses aluminum plasma as an example, commonly found in laser ablation and processing. Four research schemes were designed (using two partition function cutoff criteria-NIST data/Griem’s theory, considering/not considering the lowering of ionization energy) to calculate the partition functions, particle number densities, and line radiation coefficients of aluminum atoms and ions over a temperature range of 3000–30000 K. The results indicate that the lowering of ionization energy significantly influences the radiation properties of aluminum plasma, compared to the influence of the cutoff criteria. Therefore, accurate radiation calculations require consideration of the reduction in ionization energy. Moreover, using the straightforward approach (NIST data) for the cutoff criteria can yield temperature values with sufficient accuracy, thus simplifying the calculation of the partition function.