Investigation of laser generated plasmas expanding in vacuum and in a background gas by means of Time-Of-Flight measurements

The interest of scientific community in laser generated plasmas is constantly growing; these plasmas allow to investigate a variety of phenomena, from material science to astrophysics issues, that are the subject of our investigation; on this purpose we measured properties of an Al plasma produced with a ND:YAG laser (1064 nm, 600 mJ, 6 ns FWHM) installed at DMFCI of Catania by means of time of flight measurements obtained by using a Faraday Cup and a Langmuir Probe; the plasma expands at different background pressures. The peculiarity of our experimental set-up was that the detected voltage versus time signals were characterized at different positions away from the target surface, covering a wide range of distances; the Langmuir Probe tip was even placed just few mm from the target. This configuration permitted, other than time resolved measurements of temperature and density, to reveal some inner plasma structures that can be interpreted as ion multi-shells following fast electron layers.