Electron temperature and ionization state in laser produced plasmas

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Abstract
Neodymium glass laser pulses of up to 2 GW power, 10 ns duration and focused flux densities up to 2*1013 W cm-2 have been used to form plasmas at temperatures up to 450 eV. Plane solid plastic targets with atoms of hydrogen, nitrogen, carbon, oxygen and fluorine were used. The relation between laser flux density and electron temperature was studied and found to be of the form temperature varies as (flux density)x where x=0.40+or-0.05. Both the power law and absolute temperature are consistent with steady state hydrodynamical theories predicting x=4/9. Temperatures were deduced from soft X-ray continuum emission using both relative and absolute intensities. The spatial features of the X-ray emission were observed with a pinhole camera. Grazing incidence XUV photographic spectra were used to identify the highest degree of ionization in the plasma. The results were correlated with steady state and transient ionization theories and with the measured electron temperature. Satisfactory agreement was found when self-absorption of resonance radiation was taken into account.