Two-dimensional axisymmetric simulations of laser-produced chalcogen ion plumes using an effective plasma physics model*

Simulations of laser plasmas are essential to improve laser synthesis of novel materials. They must account for the thermo-physical properties of specific species and include 3D effects. While embedding detailed mechanisms is desirable, simulations of practical utility need to be fast and predictive. In this work we balance these demands using an effective model that incorporates standard features of laser ablation plasmas: thermal evaporation, bremsstrahlung emission, photoionization, and free-free laser absorption by the plasma. An additional effective plasma absorption coefficient is introduced as a stand-in term for other mechanisms that are impractical to account for directly—due to computational cost or unavailability of physical parameters. The effective model is constrained by Langmuir probe experimental data. The simulations are set up in a 2D-axisymmetric geometry using a solver with an adaptive Cartesian mesh. We simulate plasmas of selenium (Se) and tellurium (Te), which are of current interest in synthesis of transition metal chalcogenide materials. Predictions of Se and Te plasmas for 4 J/cm² laser fluence and 1.8 mm² laser spot area show chalcogen plumes with spatial gradients of plasma density that are steeper than those for more commonly studied copper (Cu) plumes by up to three orders of magnitude. Their spatial ion distributions have central bulges, in contrast to the edge-only ionization of Cu. The range of plasma temperatures for Se and Te is higher than for Cu by more than 0.5 eV.