Laser‐ablation‐assisted‐plasma discharges of aluminum in a transverse‐magnetic field

Abstract

Laser‐ablation‐assisted‐plasma discharges (LAAPD) have been used to enhance the ionization of laser ablated aluminum metal. Ablation is accomplished by focusing a KrF excimer laser (248 nm, 40 ns, ≤0.4 J) on a solid aluminum target with a fluence of 4 J/cm2. Peak plasma discharge voltage is 1–4 kV and peak plasma current is 0.2–1 kA, while peak power is 0.1–1 MW. Gated emission spectroscopy is used to determine the charge states and the electronic temperatures within the plasma discharge. With unmagnetized discharge parameters of 3 kV and 760 A, the observed light emission is dominated by transitions from Al2+ ions indicating nearly complete ionization of the plume. From the emission spectra intensities, an Al2+ electronic temperature of 3.3 eV is determined. Emission spectra from unmagnetized LAAPD of 1.2 kV and 280 A show no visible Al2+ ion transitions indicating cooler plasma and a lower ionization state. Introducing a 620 G transverse magnetic field (at 1.2 kV, 280 A) enhances the ionization due to the increased electron confinement and leads to the observance of the Al2+ lines as seen with discharges of 3 kV and 760 A.