PNNL

Abstract

Measurement of the temporal evolution of laser-produced plasma temperature is very important for many of its applications and several plasma diagnostic tools are routinely used by researchers. However, the accuracy and information obtained from the temperature measurement can be impacted by several parameters, including the measurement method used, uncertainty in spectroscopic constants, spatio-temporal averaging, homogeneity of the plasma, self-absorption, self-reversal, and the validity of assumptions involved such as state of thermodynamic equilibrium. In this study, we combined emission and laser absorption spectroscopy (LAS) to compare the excitation temperatures of a laser-produced uranium plasma system. Several U I transitions in the NIR spectral range (775-800 nm) were considered, and the Boltzmann plot method was used to measure the excitation temperatures using both emission and absorption spectroscopy. Emission spectroscopy provided early-time temperature measurements of the plasma up to times $\le$ 20 $\mu$s, while absorption spectroscopy provided temperature measurements at late times of plasma evolution (for times $\ge$ 5–40 $\mu$s). Comparisons of LAS and emission-based time-resolved excitation temperatures demonstrated good agreement.