Laser irradiated atomic clusters: resonant heating, high energy ions and fusion yield

Abstract

Summary form only given. Clusters are van der Waals bound solid density atomic aggregates formed in cooled gas jets. When irradiated with laser pulses the clusters ionize and explode giving rise to interesting non-linear phenomenon such as generation of high-energy electrons and ions, higher harmonics, and fusion neutrons. Our simulations indicate that laser pulse duration and intensity as well as cluster material properties determine the explosion dynamics of laser-heated clusters with consequences for potential applications. We study the heating of a single cluster by a strong laser field using an electrostatic particle-in-cell (PIC) code in the range of laser-cluster parameters such that kinetic as well as hydrodynamic effects are active. Heating is dominated by a collision-less resonant absorption process that involves energetic electrons transiting through the cluster. A size-dependent intensity threshold defines the onset of this resonance. It is seen that increasing the laser pulse width lowers this intensity threshold and the energetic electrons take multiple laser periods to transit the cluster instead of one laser period. We will present calculations showing the effect of pulse width on the heating rate and the evolution of the electron phase space. Cluster ions are accelerated by the space charge field created by the extraction of energetic electrons. However, our simulations also show that strong electron heating is accompanied by the generation of a high-energy peak in the ion energy distribution function simultaneous to an inward moving ion-density compression wave. The mechanism by which mono-energetic high-energy ions are produced will be presented. Energy spectra of ions play a vital role in ion fusion rate and generation of neutrons for possible medical, optical or sensor applications. The ion energy distribution is used to calculate the yield of thermonuclear fusion neutrons from exploding deuterium clusters using the PIC model with periodic boundary conditions that allows for the interaction of ions from neighboring clusters. We will present our simulation results showing the effect of laser pulse intensity and resonant heating on neutron yield