Expansion of a laser produced plasma into a vacuum

Radiation from a ruby laser with a maximum power of 80 MW (total energy of 1.2J) is focused on to a tip of a filament of polyethylene (CH 2 ) n with a size of 0.2*0.2 mm 2 suspended in a vacuum. About one-tenth of the total energy is absorbed in the target. Measurements are performed with an ion energy analyzer (Eubank and Wilkerson, 1963) set up at an angle of 90 degrees from the laser incidence and with an electrostatic probe with twin electrodes. The ion species in the plasma is C 2+ only. The distribution of ion energy has a peak at an energy of about 70 eV. A lack of hydrogen species is similar to the results obtained in the case of a lithium hydride plasma (Mattioli and Veron, 1969). It is found by mass analysis of the residual gas that the molecular hydrogen and methane components increase noticeably after a laser shot. The angular dependence of the expanding plasma is observed by measuring ion saturation currents to the probe. No magnetic field is applied.