VACUUM-ULTRAVIOLET SPECTROSCOPY STUDY OF EXCIMER-LASER-GENERATED PLASMAS

The dispersed emission in the vacuum ultraviolet (VUV) (1200-3000 angs trom) from the plasma generated by the interaction of a KrF excimer la ser with an Al and a YBa2Cu3O7 target has been measured. Emission spec tra were collected as a function of distance above the target surface and as a function of laser fluence. The qualitative features of the pl asmas from the two different targets were similar. The character of th e emission spectra changed from a pseudocontinuous emission at the tar get surface to discrete emission from singly, doubly ionized species a s well as neutrals at distances greater than approximately 1.5 mm. The spatial variation indicated two regions: a high-density sheath along the target where the core emission is close to blackbody; and beyond, a plasma with large opacity emitting a UV spectrum of intensity decrea sing fast with distance. Estimates of the plasma temperature and densi ty were between 2 and 4 eV and approximately 10(18)/cm(3), respectivel y.