Charge and energy transfer in argon-core–neon-shell clusters irradiated by free-electron-laser pulses at 62 nm

The multiple ionization of Ar-core–Ne-shell clusters in intense extreme-ultraviolet laser pulses ($\lambda \sim 62$ nm) from the free-electron laser in Japan was investigated utilizing a momentum imaging technique. The Ar composition dependence of the kinetic energies and the yields of the fragment ions give evidence for charge transfer from the Ar core to the Ne shell. We have extended the uniformly charged sphere model originally applied to pristine clusters [Islam et al., Phys. Rev. A 73, 041201(R) (2006)] to the core-shell heterogeneous clusters to estimate the amounts of charge and energy transfers.

Figure 1

$m/q$ spectra for $\langle N\rangle =1000$ clusters. (a) Ne pure clusters, (b) Ar-core–Ne-shell clusters produced from 1$\%$ Ar-Ne premixed gas, and (c) Ar-core–Ne-shell clusters from 3$\%$ Ar-Ne gas. The respective backgrounds are subtracted.

Figure 2

Kinetic-energy distributions of Ne${}^{+}$ and Ar${}^{+}$ from (a) Ne clusters, (b) core-shell clusters from 1$\%$ Ar-Ne, and (c) core-shell clusters from 3$\%$ Ar-Ne. The observed kinetic-energy spectra are shown by symbols (open circles for Ne${}^{+}$ ions and red open triangles for Ar${}^{+}$ ions) and the simulated kinetic-energy spectra are plotted with lines (black lines for Ne${}^{+}$ ions and red lines for Ar${}^{+}$).

Figure 3

TOF spectrum for Ar-core–Ne-shell clusters ($\langle N\rangle =1000$) produced from enriched ${}^{22}$Ne (solid line) is compared with that produced from natural abundant Ne (dotted line). The Ar content in the premixed gas was 3$\%$ in both cases, and the spectra were recorded at 24.3 eV with weak FEL intensity ($\sim$10${}^{11}$ W/cm${}^2$). The ${}^{22}$Ne ion signals are well separated from a large peak due to (H${}_2$O)${}^{+}$.