Interaction of Argon Clusters with Intense VUV-Laser Radiation: The Role of Electronic Structure in the Energy-Deposition Process

Abstract

The response of Ar clusters to intense vacuum-ultraviolet pulses is investigated with photoion spec-troscopy. By varying the laser wavelength, the initial excitation was either tuned to absorption bands of surface or bulk atoms of clusters. Multiple ionization is observed, which leads to Coulomb explosion. The efficiency of resonant 2-photon ionization for initial bulk and surface excitation is compared with that of the nonresonant process at different laser intensities. The specific electronic structure of clusters plays almost no role in the explosion dynamics at a peak intensity larger than 1.8 x 10(12) W/cm(2). The inner ionization of atoms for resonant and nonresonant excitation is then saturated and the energy deposition is mainly controlled by the plasma heating rate. Molecular dynamics simulations indicate that standard collisional heating cannot fully account for the strong energy absorption.

Heterogeneous clusters as a model system for the study of ionization dynamics within tampered samples

“…Their physical properties put them on the border between solid state and gas phase. Clusters are excellent objects to test the dynamics of samples irradiated with shortwavelength radiation from free-electron lasers (FELs) [1][2][3][4][5][6][7][8][9][10] and from high-harmonic-generation sources [11]. By studying the dependence of the cluster response on the cluster size, the influence of the atomic and condensed-matter effects on the ionization dynamics can be explored.…”

Free Electrons Generation in the Interaction of Intense Laser Pulses with Atomic Clusters

“…This occurs during collisions between electrons released from individual atoms but remaining bounded by the cluster as a whole (by cluster ions). This inverse bremsstrahlung process is a very effective way of the laser energy deposition in the cluster [12,13]. Next, the quasi-free electrons inside the cluster gain enough energy to overcome the Coulomb potential barrier.…”

“…The short-wavelength photons with energy sufficient to ionize isolated xenon and almost sufficient to ionize argon atoms were generated by a free-electron laser. The cluster explosion and ionization mechanisms in this frequency regime [11][12][13] turn out to be very different from that known from the infrared and optical pulses [14,15].…”

“…Only recently reports on the interaction of clusters with short--wavelength pulses in the vacuum ultraviolet frequency range appeared [11,12]. The short-wavelength photons with energy sufficient to ionize isolated xenon and almost sufficient to ionize argon atoms were generated by a free-electron laser.…”

“…), and temporal full width at half maximum of 50 fs. These parameters were used in the experiments [12] and in our previous theoretical paper [13].…”