Pressure dependence of enhanced x-ray line emission from laser-produced plasmas expanding in an ambient gas

An experimental study of parametric dependence of space-resolved x-ray line emission from laser-produced magnesium plasma expanding in a helium background gas has been performed for different pressures up to 125 mbar. A strong enhancement in MgXI He-alpha resonance (1s(2) S-1(0)-1s2p(1)P(1) at 9.17 Angstrom) and intercombination (1s(2) S-1(0)-1s2p(3)P(1) at 9.23 Angstrom) line emission is observed in the expansion region extending up to similar to 6 mm from the target. At the optimum background gas pressure of about 40 mbar, there is an order of magnitude increase in the x-ray line intensity compared to that observed for a gas pressure of few mbar. The results of measurements of the distance of the peak emission region from the target and width of the emission zone for different pressures are presented, and the role of the background gas for the observed behavior is discussed. (C) 2003 American Institute of Physics.