On the direct observation of the gas-dynamics of laser-pulse sputtering of polymers

Direction-selective free expansion of laser-produced plasmas from planar targets

Direction-selective expansion of laser-produced plasmas from planar slab targets of Al, Ni, Mo, and Ta are reported. Angular distributions of the particles emitted from the targets, produced by a 130 mJ, 5 nsec, Nd:YAG laser, were obtained by means of a retarding potential analyzer and a quartz crystal. It was observed that the angular distributions of the particles had mainly three characteristics. For a given laser energy and a given target element, the angular distribution showed more preferential focusing toward the target normal as the value of the focal spot size B increased. Second, for a given laser energy and a given focal spot size, the focusing was more pronounced toward the target normal as the atomic mass number of the target materials increased. Third, for a given energy, a given focal spot size and a given element, the particles with higher ionization states were much more focused toward the target normal. Our experimental results confirm the Monte Carlo simulation results of the earlier works taking into account collision and recombination processes.

Time of flight measurements on ion-velocity distribution and anisotropy of ion temperatures in laser plasmas

Using a 200-mJ, 5-ns, Nd:YAG laser (where YAG denotes yttrium aluminum garnet), time of flight spectra for ions produced from slab targets of carbon, aluminum, nickel, and tantalum were obtained at a laser intensity of approximately 5x10(10) W/cm(2). The velocity distribution function of ions of each ionization state, at several angles, in the plane of incidence, was investigated and was observed to depart significantly from the Maxwell-Boltzmann distribution function. Kinetic temperatures of ions of each ionization state were estimated separately at various angles in the plane of incidence and were observed to show a highly anisotropic property leading one to conclude that the equipartition of energy between the plasma electrons and ions has not taken place. The results are discussed and the relevant conclusions are presented.