Ultrashort pulse laser produced plasmas

Abstract

The interaction of an ultrashort pulse laser with planar aluminum targets and with layered aluminum/silicon targets is investigated with a non‐LTE radiation hydrodynamics model. The energy deposition for an obliquely incident P‐polarized laser beam is calculated with a Helmholtz wave equation. A fraction of the absorbed energy is expended in the production of fast electrons, which are transported and deposited in the cold target. These electrons produce K‐shell vacancies which produce characteristic Kα line radiation. The atomic models include the ground states and an extensive manifold of excited states for each of the materials in the target. The ionization dynamics is calculated with a time dependent collisional radiative model self‐consistently coupled to a probabilistic radiation transport scheme. The emitted x‐rays, including the Kα radiation, provide information about the energy deposition in the target, the energetic electron spectrum, and the time dependence of the local ionization in the target. The focus of the investigation is directed towards characterizing the radiative properties of the plasma, as well as determining whether the plasma can support population inversions and lasing as a result of recombination into highly ionized excited states in the rapidly cooling blowoff plasma.