CHARACTERIZATION OF A LASER-ABLATION-ASSISTED PLASMA DISCHARGE METALLIC ION-SOURCE

Experiments have been carried out to characterize further the properti es of a new laser-ablation-assisted-plasma-discharge source of metalli c aluminium ions. Laser ablation is accomplished by focusing a KrF exc imer laser (<1.2 J, 40 ns, 248 nm) onto a solid aluminium target with a fluence of approximately 10 J cm(-2). Through gated optical emission spectroscopy, the laser ablation plume optical emission is observed t o contain only aluminium neutral atom transitions after approximately 100 ns, With the application of a 3.6 kV, 760 A discharge, the neutral atom plume is transformed into a plasma with the emission dominated b y Al+ and Al2+ ion transitions. Through time-resolved spectroscopy, em ission intensity from the Al neutral species and the Al2+ ion species is observed to coincide with current peaks through the plasma. Spectro scopic measurements indicate an Al2+ electronic temperature of 3 eV (a nd an Al+ electronic temperature of 1 eV) which, since local thermodyn amic equilibrium (LTE) is applicable for the observed emission, provid e a free electron temperature of 1 to 3 eV. A simple LTE model suggest s an electron temperature of 1.2 eV for equal Al+ and Al2+ ion fractio ns. A floating double Langmuir probe measurement 1 mm in front of the laser ablation spot indicates an electron temperature of roughly 1 eV and an ion density of approximately 5 x 10(14) cm(-3) during the secon d current lobe.