Coulomb Explosion in Nanosecond Laser Fields

Abstract

We report experimental observations of Coulomb explosion using a nanosecond laser at 532 nm with intensities less than 10 12 W/cm 2 . We observe multiply charged atomic ions Ar n+ (1 ≤ n ≤ 7) and C n+ (1 ≤ n ≤ 4) from argon clusters doped with molecules containing aromatic chromophores.The yield of Ar n+ depends on the size of the cluster, the number density, and the photostability of the dopant. We propose that resonant absorption of Ar N + achieves a high degree of ionization, and the highly positively charged cluster has the capability to strip electrons from the evaporating Ar + on the surface of the cluster prior to Coulomb explosion, forming Ar n+ .

Production of Multiply Charged Argon Ions in Moderate Nanosecond Laser Fields: An Open Question or a Forgone Conclusion?

“…Vatsa and Mathur (VM) commented on our publication titled “Coulomb Explosion in Nanosecond Laser Fields”. In a nanosecond laser field of ∼10 12 W/cm 2 , we have observed Ar n + (1 ≤ n ≤ 7) and C n + (1 ≤ n ≤ 4) from argon clusters containing an aromatic chromophore such as fluorene or halogenated fluorenes . The statements of VM on the difficulties facing the explanation of the experimental results, i.e., extensive production of multiply charged atomic ions (MCAIs) in laser fields orders of magnitude lower than those typically considered possible, are in agreement with our assessment of the situation.…”

“…Among the three major points raised by VM, we are in full agreement with the authors on the limited role of the chromophore and the beneficial effect of resonance for the formation of Ar + . In the introduction of our Letter, references to a variety of compounds investigated by three other groups are listed, − and the lack of a common structural motif among the compounds implies that a chromophore is not the prerequisite to observe MCAIs. Our path of ionization for Ar + is specific only to our own experiment and is not intended to be general: the path with the resonances is the enhanced path, offering a higher probability of excitation than otherwise.…”

Generation of Multiply Charged Argon Ions in Nanosecond Laser Field Ionization of Argon Clusters

“…Furthermore, the high energy of ionizing photons would also ensure that the photoelectrons generated in their experiment would have a large kinetic energy and some, if not all, will leave the cluster, leaving its surface charged in similar fashion to that hypothesized by Zhang and coworkers. 1 Crucially, Fennel et al were unable to observe any multiply charged argon ions in their experiments, 12 in contradiction to the expectations of the evaporation model of Zhang and coworkers. It is particularly noteworthy that in an extension of their initial experiment, Fennel et al employed a two-pulse scheme wherein Ar-clusters were initially ionized by the XUV beam, and then subsequently irradiated by a near infrared beam which was temporally delayed by 5 ps.…”

“…8,10,15,16 We also wish to draw attention to an unexpected facet reported by Zhang and coworkers in their Supplementary Material. 1 It appears that the externally applied DC field (used to extract ions from the laser-cluster interaction zone) is immaterial as the same charge distributions are obtained in presence of an external DC field as well as while using delayed extraction. So, the field that appears to be of primary importance in the experiments of Zhang and coworkers is that due to the presence of ions.…”

Development of ion recoil energy distributions in the Coulomb explosion of argon clusters resolved by charge-state selective ion energy spectroscopy

“…The ionization dynamics of rare gas clusters are in the focus of experimental studies [10,[13][14][15][16][17][18][19]. To date, only a few experiments aimed to resolve the underlying charge-state distributions upon exposure to strong optical laser fields [10,13,14].…”