Comparison of excitation temperature of a laser-produced plasma by combining emission and absorption spectroscopy

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, it is very challenging to measure the properties of the plasma at the early and late times of its evolution using a single diagnostic tool. In this study, we combined emission and laser absorption spectroscopy to compare the excitation temperatures of a laser-produced uranium plasma system. Several U I transitions in the near-infrared 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 2–20 µs, while absorption spectroscopy provided temperature measurements at late times of plasma evolution (for times 5–80 µs). The emission and absorbance of U I transitions were found to follow the Boltzmann distribution, indicating the plasma is likely in the state of local thermodynamic equilibrium even at late times of its lifetime. The emission and absorption-based time-resolved excitation temperatures demonstrated good agreement at earlier times (≤15 µs) in the overlapped temporal region, while a deviation in the measured values was seen at times (≥15 µs), and potential reasons for such a disagreement are discussed.

The role of laser wavelength on the early-stage electron density evolution in laser-produced plasma

“…7 In each application, understanding how the plasma properties evolve over the plasma lifecycle is important for the optimization of various plasma attributes such as conversion efficiency, line emission, nanoparticle generation, and various others. 8,9 However, most studies typically focus on the measurement of plasma properties during the later stages of the plasma evolution, after the plasma has thermalized (in ambient gas) or reached a state of free expansion (in vacuum). This can be attributed to a number of difficulties with taking measurements of the early plasma, including the highly transient nature of the plasma, deviations from local thermal equilibrium (LTE), high continuum emission, and other attributes.…”