Study on extreme ultraviolet spectroscopic features of temperature-dependent highly charged calcium ions

The energy level distribution and transition characteristics of highly charged calcium ions are key data for astrophysics, plasma radiation characteristic research, and EUV light sources. To deeply explore the extreme ultraviolet (EUV) spectral characteristics of highly charged calcium ions, this study employs Nd:YAG laser pulses with a wavelength of 1064 nm and a pulse width of 10 ns to ablate high-purity solid calcium targets to generate plasma. High-resolution EUV spectrometers are used to obtain spatially and temporally resolved spectra in the 8‒14.5 nm wavelength range. Theoretical calculations are conducted using the Cowan program based on relativistic Hartree‒Fock configuration interaction. Characteristic emission lines of highly charged calcium ions (Ca7+‒Ca10+) are identified. Combined with the collision radiation model and the normalized Boltzmann distribution hypothesis, precise simulation of experimental spectra is achieved. In particular, four isolated characteristic peaks that are very sensitive to plasma electron temperature are discovered, which are expected to become “probes” for real-time diagnosis of plasma states.