Effect of laser pulse time profile on its absorption by argon clusters

Abstract

The interaction of medium sized Argon clusters (30 Å) with high-intensity femtosecond laser pulses (806 nm, 8 × 1016 W/cm2) of durations ranging from 10 fs to 120 fs have been studied using a three-dimensional relativistic time dependent molecular dynamic approach. The dynamics of cluster expansion is explained in terms of temporal evolution of electron population in the cluster and snapshots of particle positions at various times. The effects of inter-cluster distance on ionization dynamics are presented. It is observed that the collisional ionization increases with decreasing inter-cluster distance. The effect of pulse duration on laser energy absorption is also studied. For a laser pulse of gaussian time profile, there exists an optimum pulse duration for maximum absorption. No such optimum exists for a nearly flat top (super-gaussian) laser pulse. Results indicate the existence of resonance absorption inside the cluster. It is also observed that the high energy component of ion emission from cluster is anisotropic, showing a preferential direction of emission along laser polarization while the low energy ions emerge almost isotropically.