ABSTRACT
Results of comparative VIS-IR spectroscopy measurements of zinc (Z=30) and Cu (Z=29) plasmas are presented. The measurement was part of a more complex experiment aimed at the characterisation of plasmas generated by ~400 ps laser pulses producing net irradiance in the range of 4x1011 - 1011 Wcm-2, equivalent to those produced by weak prepulses in some collisional systems. The obtained spectra of both Zn and Cu are rather dominated by lines belonging to the neutral and the singly ionised states. This is rather surprising even for the highest irradiance. It can be attributed to the fact that lines of lower ionisation states are biased in thfi spectra due to the emitting volume and emission duration of cold, slowly recombining plasma. The effective (time-and space-integrated) electron temperatures inferred from the spectra are very similar for both elements, at ~5 eV for the highest irradiance. The results are briefly discussed with regard to the physics of preplasmas generated by weak prepulses.
