Intense Laser-Cluster Interaction: Effect of hot electrons on propagation and studies with longer pulse widths

The non-linear interaction of intense short laser pulses with gases of atomic clusters has applications in areas such as x-ray and energetic particle generation, and nuclear fusion. We model the propagation of laser pulses through a medium of Argon clusters (14 to 54 nm diameter) and un-clustered Argon atoms. Our goal is to understand the competing effects of the non-linear dielectric response of the clusters and that of the free electrons on self-guiding. In our propagation model, the effective dielectric constant of the medium evolves in time due to the hydrodynamic expansion of clusters, ionization of un-clustered monomer gas atoms as well as due to the creation of `hot' electrons during the laser-cluster interaction. Hot electron generation is based on the PIC simulation of laser-cluster interaction[1]. Our simulation results show that for moderate intensities $\sim $6$\times $10$^{15}$ W/cm$^{2}$ the hot electrons lead to enhancement in self-guiding. We also investigate the dynamics of cluster explosion for a range of pulse lengths. Preliminary results suggest that early in the pulse cluster expansion is governed by hydrodynamic forces while kinetic effects dominate later in the pulse. [1] T. Taguchi et. al. PRL \textbf{92}, 205003 (2004).