Fast-beam study of H₂⁺ions in an intense femtosecond laser field

Abstract

A fast beam of H2+ ions, produced from a low energy ion accelerator, has been used for the first time in intense laser field experiments. The technique has enabled neutral dissociation products to be analysed and detected for the first time in such studies. Energy spectra of neutral and ionized fragments, product yields as a function of focused laser intensity and angular distributions of neutral dissociation products have been measured. Significant differences are observed between the present results and those obtained from experiments involving neutral H2 molecules. These differences are indicative of the precursor H2 molecule playing an important and hitherto neglected formative role in the laser-induced fragmentation processes.

Quantitative theory-versus-experiment comparison for the intense laser dissociation ofH2+

“…The argument retained by doing so, is that asymptotically, due to R A different situation prevails in the experiments of the second family where an electric or a plasma discharge ionizes H 2 into H + 2 [13,16]. The resulting ion beam is strongly accelerated by an electric field and is crossed at t = 0 by the laser beam at a point O of the laboratory frame.…”

“…The independence of the ionization and dissociation processes can not be experimentally controlled, and their competition is still an open question [5]. More recently, another kind of approach has been investigated through ion beam experiments, where H + 2 ions are produced in a dc electric or plasma discharge that disentangle ionization and dissociation processes [13,16]. An accelerated and strongly collimated monochromatic H + 2 beam is crossed at right angle by a focused intense laser beam.…”

Suppression of Multiple Ionization of Atomic Ions in Intense Ultrafast Laser Pulses

“…DOI: 10.1103/PhysRevLett.88.233001 PACS numbers: 32.80.Fb There is considerable current interest in the interaction of high intensity ͑10 13 10 18 W cm 22 ͒ radiation with dilute matter, where the external electric field strength becomes comparable to molecular bond and valance electron binding strengths. Studies have been carried out with targets of atoms, molecules, clusters [1], and most recently molecular ions [2,3], in order to elucidate the new physics observable in this highly nonlinear regime. These include the study of high harmonic generation [4], strong field effects in molecular dissociation, and the enhancement of multiple ionization in atoms [5,6].…”

“…By contrast our experiment is capable of studies using a fast beam of atomic positive ions, in addition to neutral atoms, as a target. Our apparatus has recently been used to yield new and unambiguous insights into the fragmentation dynamics of H 1 2 in a strong laser field [2]. A previous attempt to study the interaction of atomic ions in intense laser fields used in fact neutral targets, but assumed that the ions were formed well before the laser pulse reached its maximum [24].…”

“…Studies have been carried out with targets of atoms, molecules, clusters [1], and most recently molecular ions [2,3], in order to elucidate the new physics observable in this highly nonlinear regime. These include the study of high harmonic generation [4], strong field effects in molecular dissociation, and the enhancement of multiple ionization in atoms [5,6].…”