X-ray line emission from H-like and He-like ions in magnesium plasma produced by multi-picosecond laser pulses

We report a spectroscopic study of x-ray line emission from a magnesium plasma produced by Nd:glass laser pulses of 30 ps (FWHM) duration at a laser intensity of ~ 3 x 1014 Wcm-2. High-resolution x-ray line spectrum was recorded using a crystal spectrograph. Measurements of continuum radiation intensity were also performed for different x-ray filter cutoff energies. A peak electron temperature of ~ 2.4 keV derived from these measurements is in agreement with that calculated from an analytical model describing laser plasma heating in the short pulse regime. The intensity ratio of MgXII 1s-2p, λ = 8.42 Å and MgXI 1s2-1s2p, λ = 9.17 Å is observed to be much smaller than that calculated from the spectroscopic code RATION. Analytical estimates of ionization equilibrium time for different ionization states in the heated plasma as well as during its expansion using a simple hydrodynamic model can explain this behavior.