Electron beam ablation versus laser ablation: plasma plume diagnostic studies

Abstract

Experiments have been performed to compare XeCl laser ablation plume characteristics to those produced by electron beam ablation. Potential advantages of electron beams include higher electrical efficiency (∼30%), and the ability to process materials with high optical reflectivity or transparency. The electron beam is generated by a channelspark with parameters: peak voltage of 15–20 kV, current of 1.5–1.7 kA, and pulse length of about 200 ns. The electron beam is ion focused to about 2 mm diameter by an argon background gas. Initial diagnostic experiments have utilized optical emission spectroscopy to characterize the ionization dynamics of the ablation plumes of Fe targets. Spectra taken during electron beam ablation are composed of singly ionized iron, with negligible emission from neutral iron. This is in sharp contrast with XeCl excimer laser ablation, which is composed of both neutral and ion species, the neutrals persisting strongly after the laser pulse. In addition to Fe ion emission, the channelspark emission spectrum also exhibits a high degree of excitation and ionization of the Ar background gas. Strong emission from Ar +, Ar 2+, and Ar 3+ has been measured.