Simulations of femtosecond laser pulse interaction with spray target

Abstract

Laser interactions with spray targets (clouds of submicron droplets) are studied here via numerical simulations using two- dimensional particle-in-cell codes. Our simulations demonstrate an efficient absorption of laser pulse energy inside the spray. The energy absorption efficiency depends on the inter-droplet distance, size of the cloud of droplets, and laser pulse intensity, as well as on the pre-evaporation of droplets due to laser pulse pedestal. We investigate in detail proton acceleration from the spray. Energy spectra of protons in various acceleration directions vary significantly depending on the density profile of the plasma created from the droplets and on laser intensity. The spray target can be alternative of foil targets for high intensity high repetition ultrahigh contrast femtosecond lasers. However, at intensities >10^21 W/cm2, the efficiency of laser absorption and ion acceleration from the droplets drops significantly in contrast to foils.