Electron temperature and ionization state in laser produced plasmas

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.

X-Ray Emission from Laser-Produced Plasmas

“…Both these x-ray interests are extensions of work done in the uv and extreme ultraviolet regions using lower-power lasers and often low-atomic-number targets. 18,19 The appearance of intense spectra in the 1-2 keV range immediately indicates that the plasma electron temperatures are ~0.5 keV. Acutally, the temperature is a rapidly varying function of both time and spatial coordinates, but the concept of a single, effective temperature is useful albeit approximate.…”