Observation of a 6p-6d giant dipole resonance in the VUV photoabsorption spectrum of a laser-produced thorium plasma

We have measured the VUV photoabsorption spectrum of a thorium plasma produ ced by the laser irradiation of a metal target. At times in excess of 600 n s after plasma initiation, the plume is dominated by neutral atoms and a 6p -6d giant dipole resonance is observed in the spectrum. These first VUV ato mic data in the 17-32 eV energy range are compared with existing solid-stat e data and theoretical calculations.