Spectroscopic analysis of the excitation transfer from background air to diffusing aluminum laser produced plasma

Abstract

During the relaxation of the plasma plume generated by laser ablation of an aluminum target, a pronounced intensity enhancement is observed at the central wavelength of the 396.15 nm self-reversed resonant line. This spectral special feature is analyzed and related to the interaction of the plasma edge with the background air excited by the shockwave, prompt electrons, and extreme ultraviolet radiation produced at the earliest times of the ablation. In this article, the electron density, the aluminum ground state, and resonant level populations are determined from the fitting of the 396.15 nm calculated line profile to the experimental one at two background pressures (100 and 1000 Pa). The evolution of these densities is derived from experiments performed at delays, after the laser pulse arrival, ranging from 120 to 180 ns.

Dynamical plasma study during CaCu3Ti4O12 and Ba0.6Sr0.4TiO3 pulsed laser deposition by local thermodynamic equilibrium modelling

“…As it can be seen on table 4, temperature and density decrease slowly and maintain an important ionization rate in a large volume. Temperatures and electronic densities estimated from this model are in good agreement with values from the literature obtained with other simulation approaches applied to similar experimental conditions [5,9,[16][17][18].…”

Analysis of relaxing laser-induced plasmas by absorption spectroscopy: Toward a new quantitative diagnostic technique

“…We previously arrived at the same conclusion when the laserinduced absorption experiments were performed under lower ambient pressures [10]. The confinement of the ablated species by the surrounding gas reduces the speed of the expansion but, even at atmospheric pressure, the corresponding transport time remains much shorter than the ionic recombination one.…”

“…For instance, Hermann et al [20] have developed a plasma emission model based on a two-temperature scheme, in which the plasma was assumed to have two uniform zones of different temperature and electron number density. Trapezoidal distributions have been successfully tested to simulate aluminum self-reversed lines [10]. Karabourniotis et al [23] have suggested original distribution functions depending on different "shape factors".…”

“…It is interesting to compare the corresponding characteristic decay times (τ e for electrons and τ l for atoms) to the characteristic time τ trans of the plume expansion: considering the plasma as an expanding sphere (volume V e ), τ trans can be derived from the temporal evolution of the σ e (t) plume width through the expression [10]: …”

“…In nanosecond laser ablation, the evaporated atoms are significantly ionized through multi-photon ionization and inverse Bremsstrahlung [4,5] and the high-temperature and high-pressure vapor expands into a shockwave [6], with emission of fast prompt electrons [7,8], and XUV radiation [9]. The relaxation phase of the plasma includes other complex processes: quenching of the ablation products among themselves and with ambient gas molecules, propagation of the plume and gas phase chemical reactions [10,11]. Thanks to the great strides made in electronics and optics during the last decade, it is now possible to achieve the measurement of the temporal and spectral emission characteristics of expanding laser-induced plasmas.…”