The Plasma Parameters of a Bimetallic Laser Plasma: Experiment and Simulation

Pulsed laser deposition (PLD) is a versatile technique for nonequilibrium growth of materials of complex stoichiometry. Kinetic manipulation of materials processing in PLD requires controlling the plasma parameters of its chemically complex and transient plasma flows. Here we compare trends in the plasma parameters measured for a laser plasma with predictions from a laser ablation/plasma fluid expansion simulation. Langmuir probes were used to measure the electron density, the electron temperature, and the Mach number of the plasma expansion. The fluid simulation accounts for singly and doubly charged ions, as well as electrons and neutrals, and is carried out in a multidimensional setting using a state-of-the-art, open-source adaptive Cartesian mesh framework. Experiment and simulation investigate a bimetallic plasma containing iron (Fe) and selenium (Se), obtained by ablating a solid pellet of FeSe with the 25 ns pulse of a KrF excimer laser (248 nm). For laser spot areas below 4.5 mm², the peak values of the experimental electron density, electron temperature, and Mach number of the expansion all increase gradually when laser fluence is in the 0.5-4.0 J/cm² range. The same trend is reproduced in the simulation. We will discuss how the measured time dependence of the plasma parameters can be used to constrain the simulation and test mechanisms of laser plasma formation that need to be invoked for accurate predictions of PLD plasmas containing multiple chemical species.