Investigation of laser-produced plasmas from metal-surfaces

The output beam of a Ruby Giant Pulse Laser (30 nsec halfwidth, up to 100 MW peak power) was focussed onto the surface of aluminium and copper-targets, which were cleaned by heating them to 500 degrees C at 10 -7 torr. The evaporated ions and electrons were detected at a distance of 170cm away from the target, after having passed some retarding grids. By a combination of time of flight- and retarding potential measurements the different charged ions could be separated and their energy distribution and intensity ratios were measured. his yields information simultaneously about the kinetic ion energies and the plasma electron temperature. It turns out, that the mean kinetic energy of the ions is proportional to their charge and about 100 times larger than their thermal energy. The experimental results and their interpretation in connection with the mechanisms of plasma generation and heating by laser light are discussed and compared with theoretical and experimental investigations of other authors.