Strong-field ionization and fragmentation of large, gas-phase clusters in the few-cycle domain

TL;DR

This study investigates how ultra-short, intense laser pulses affect large argon clusters, revealing unique ionization dynamics, lower ion energies, and anisotropic ion yields due to rapid Coulomb explosion and electronic shielding effects.

Contribution

It demonstrates the distinct ionization and fragmentation behavior of large clusters under few-cycle laser pulses, highlighting differences from longer pulse regimes and introducing new insights into anisotropic ion emission.

Findings

Ion energies are lower with 10 fs pulses compared to 100 fs pulses.

Ion yields are significantly higher perpendicular to laser polarization.

Cluster dynamics are dominated by rapid Coulomb explosion with minimal expansion.

Abstract

Intense 3-cycle pulses (10 fs) of 800 nm laser light are utilized to measure energy distributions of ions emitted following Coulomb explosion of Ar$_n$ clusters ($n$=400-900) upon their irradiation by peak intensitis of 5$\times$10$^{14}$ W cm$^{-2}$. The 3-cycle pulses do not afford the cluster sufficient time to undergo Coulomb-driven expansion, resulting in overall dynamics that appear to be very different to those in the many-pulse regime. The peak ion energies are much lower than those obtained when 100 fs pulses of the same intensity are used; they are almost independent of the size of the cluster (over the range 400-900 atoms). Ion yields are a factor of 20 larger in the direction that is perpendicular to the laser polarization vector than along it. This unexpected anisotropy is qualitatively rationalized using molecular dynamics calculations in terms of shielding by an electronic charge cloud within the cluster that is spatially asymmetric.