Dead-time-free ion momentum spectroscopy of multiple ionization of Xe clusters irradiated by euv free-electron laser pulses

We have investigated multiple ionization of Xe clusters by 61-nm ${10}^{11}–{10}^{12}\text{W}/{\text{cm}}^2$ extreme-ultraviolet light pulses at the free-electron laser facility, SPring-8 Compact SASE Source test accelerator, in Japan, using a dead-time-free three-dimensional momentum spectrometer. It was found that the average kinetic energy of atomic ${\text{Xe}}^{+}$ ions increases when increasing the laser power density and the cluster size. For these experimental conditions significant frustration of the cluster photoionization occurs but no indication for heating mechanisms other than sequential photoabsorption by individual atoms in the cluster was found.

Figure 1

(Color online) Experimental configuration.

Figure 2

(Color online) Kinetic-energy distributions of ${\text{Xe}}^{+}$ ions emitted from Xe clusters, (a) measured for $⟨n⟩\sim 150$ at three different FEL power densities of 1.3, 5.2, and $13\times {10}^{11}\text{W}/{\text{cm}}^2$ and (b) simulated for ${\text{Xe}}_{150}^{Z+}$ by a classical molecular-dynamics (MD) calculation.

Figure 3

(Color online) Kinetic-energy distributions of ${\text{Xe}}^{+}$ from Xe clusters, (a) measured for $⟨n⟩\sim 50$ and $\sim 200$ at $5.2\times {10}^{11}\text{W}/{\text{cm}}^2$, (b) simulated for ${\text{Xe}}_{200}^{Z+}$, and (c) simulated for ${\text{Xe}}_{50}^{Z+}$.