A SPECTROSCOPIC STUDY OF PLASMAS PRODUCED BY LASER-ABLATION OF HOLLOWALUMINUM TARGETS

In this paper we report the study of plasmas generated when the laser beam hits a target surface in the middle of a hole through the target, the diameter of the hole being slightly smaller than the laser beam's waist. The hole's axis coincides with the laser beam's axis. In such a case two plasma clouds are observed: one expands from the front hole opening towards the laser, the other from the back side of the target in the opposite direction. The experiments indicate that the plasma i n front of the target is similar in appearance to the plasma generated by ablation of a planar surface. On the other hand, the plasma behind the target is significantly less dense and is also much colder than t he corresponding plasma in front of the target.