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Ion charge state distribution in the laser-induced Coulomb explosion of argon clusters

Ion emission resulting from the Coulomb explosion of highly charged Ar40 000 clusters is studied experimentally and by means of three-dimensional microscopic particle-in-cells (3D-MPIC) simulations, for laser intensities up to 1016 W cm−2. The experimentally measured ion emission spectrum shows a pronounced knee-like feature which defines the maximum energy of isotropically emitted ions in the Coulomb explosion. The variation of the ‘knee energy’ with laser intensity that is measured in our experiments is rationalized using 3D-MPIC simulations. The computations also enable an estimate to be made of the ion charge distributions. The computations show that at a laser intensity of 1016 W cm−2, more than 64% of the ions that are produced are in very high charge states (8+ or higher).