Spectroscopic Characterization of Uranium Laser Produced Plasma

There are several spectroscopic methods for measuring the temperature of a laser-produced plasma system. Depending on the technique used, the excitation, electron, ion, neutral, molecular (vibrational and rotational), or kinetic (translational) temperature of the plasma can be measured. If the plasma system is homogeneous and in local thermodynamic equilibrium, each temperature will be approximately equal. However, LPP systems are inhomogeneous in time and space which can lead to differences in measured temperatures, and also deviations from LTE conditions. In this study, 1064 nm, 6 ns pulses from an Nd:YAG laser were used to generate uranium LPPs. Emission and laser absorption spectroscopy were then used to compare temperatures at early and late times of plasma evolution. Several U transitions in the NIR spectral range (775–800 nm) were used. Emission spectroscopy was used to measure excitation temperature up to times of
$< 20\mu\mathrm{s}$
. Laser absorption spectroscopy was used to measure both excitation and kinetic temperature at times
$> 5-40\mu\mathrm{s}$
. Our results showed disagreement in various measured temperatures at early times attributed to the inhomogeneous nature of the LPP system and non-LTE conditions.