Molecular dynamic studies on anisotropy of atomic cluster explosions driven by few-cycle intense lasers

Theoretical Physics Division, Bhabha Atomic Research Centre - Mumbai-400085, India

^a gauravm@barc.gov.in

Received: 23 September 2011
Accepted: 25 October 2011

Abstract

The dynamical processes following the irradiation of various argon clusters (16–58 Å) with high-intensity lasers (5×10¹⁴ W/cm²–3×10¹⁶ W/cm²) of femtosecond pulse durations (5–100 fs) are modelled using a three-dimensional relativistic time-dependent molecular dynamic approach. Various parameters governing the cluster explosion like electron population, average degree of ionization, mean energy of ions etc. are studied. For a fixed value of laser intensity and cluster size, the variation of laser pulse duration (FWHM) leads to a change in the character of the anisotropy in the ion emission. For sufficiently short laser pulses (few cycles), the yield of ions is higher along the perpendicular to laser polarization direction rather than along the parallel to the direction of laser polarization. As the pulse duration increases, this “atypical anisotropy” first grows and then reduces, indicating an optimum pulse duration for this effect. Effects of laser pulse intensity and cluster size are also investigated for this optimum value of pulse duration (∼10 fs). It is found that for a cluster size of 58 Å, the maximum observed anisotropy happens to be at an intensity of 4.5×10¹⁴ W/cm² for a pulse duration of 10 fs. This anisotropy increases with cluster size for the above parameters of intensity and pulse duration.