Double core-hole spectroscopy of transient plasmas produced in the interaction of ultraintense x-ray pulses with neon

Abstract

Double core-hole (DCH) spectroscopy is investigated systematically for neon atomic system in the interaction with ultraintense x-ray pulses with photon energy from 937 eV to 2000 eV. A time-dependent rate equation, implemented in the detailed level accounting approximation, is utilized to study the dynamical evolution of the level population and emission properties of the highly transient plasmas. For x-ray pulses with photon energy in the range of 937-1030 eV, where $1s\rightarrow 2p$ resonance absorption from single core-hole (SCH) states of neon charge states exist, inner-shell resonant absorption (IRA) effects play important roles in the time evolution of population and DCH spectroscopy. Such IRA physical effects are illustrated in detail by investigating the interaction of x-ray pulses at a photon energy of 944 eV, which corresponds to the $1s\rightarrow 2p$ resonant absorption from the SCH states ($1s2s^22p^4$, $1s2s2p^5$ and $1s2p^6$) of Ne$^{3+}$. After averaging over the space and time distribution of the x-ray pulses, DCH spectroscopy at photon energies of 937, 944, 955, 968, 980, and 990 eV (corresponding to the $1s\rightarrow 2p$ resonance energies of Ne$^{2+}$-Ne$^{7+}$, respectively) are studied in detail. The complex mechanisms of producing the DCH states are discussed, taking the DCH spectroscopy at 937 and 980 eV as examples. For photon energy larger than 1362 eV, there are no resonance absorption in the interaction, resulting in a similar physical picture of DCH spectroscopy. The dominant DCH states are due to higher ionization stages of Ne$^{7+}$-Ne$^{9+}$, while the DCH spectroscopy from lower charge states Ne$^{2+}$-Ne$^{6+}$ are much weaker. With the increase of x-ray photon energy, the contributions from the lower charge states become larger.