Space dependent recombination in a laser-produced Ta plasma

Angular dependent emission of plasma after irradiation of a solid tantalum target by a Nd-YAG Q-switched laser (I approximately=10 10 W cm -2 ) has been measured for different angles of incidence of the laser beam relative to the target normal. It is observed that the particles are preferentially emitted in the direction of the target normal, both for normal and oblique incidence. With increasing number of charge, the low-energy parts of the spectra tend to disappear, which the authors interpret as being due to recombination. For oblique incidence the emission spectra are no longer symmetrical relative to the target normal. This can be explained by the unsymmetrical heating of the expanding plasma by the laser pulse. In addition, this gradient in temperature seems to lead to a certain discrimination of three-body and radiative recombination.