Time evolution analysis of dynamics processes in laser-produced Al plasmas based on a collisional radiative model

Abstract

The temporal evolution of extreme ultraviolet emission from a laser-produced aluminum plasma has been experimentally and theoretically investigated. Spectra of highly charged Al ions have been measured by using the temporal-spatially resolved laser-produced plasma emission technique. In order to deeply understand the evolution of plasmas and achieve the purpose of rapid diagnosis, a collisional-radiative model has been resolved in the steady-state and time-dependent cases, respectively. The evolution of rate coefficients as a function of the electron temperature, electron density, and time delay has been discussed, respectively. In addition, the influence of the photo-ionization process has also been evaluated for the ionization balance. The results indicate that the time evolution analysis of spectra is useful for the accurate understanding of the evolution behavior of highly charged ions in laser-produced plasmas.

Investigation of a Collisional Radiative Model for Laser-Produced Plasmas

“…Colombant and Tonan [5] used units of cm 3 s −1 for rate coefficients for the three dominant processes and to express photoionization rates in these units Su et al considered rates/electron number density (n e ). These authors found rate coefficents for photoionization between 10 −9 to 10 −15 cm 3 s −1 depending on the electron temperature and density [10]. Other photoionization rates have been reported [11], but these rates describe multi-photon ionization during the formation of LPPs and thus are not applicable to the CR model considered here.…”

“…This minimum laser flux can be achieved easily with typical Nd:YAG lasers, with laser pulse energies, pulse widths, and focal spot diameters on the order of 1 J, 10 ns, and 100 µm, respectively. Where spot sizes are on the order of 10s of µm the minimum laser flux is greatly exceeded [6,[8][9][10]. Similarly, with T e = 3 eV and λ = 10.6 µm, a laser flux on the order of 10 7 W/cm 2 is found, which can be exceeded by laser energies, pulse widths, and focal spot diameters on the order of 1 J, 1 µs, and a few mm, respectively.…”

“…The CR model continues to be used to estimate charge state distributions for the emission spectra of a variety of elements, for example C (Z A = 6), Ge (Z A = 32), and Gd (Z A = 64) [6][7][8]. Typically in these experiments laser pulse lengths are on the order of 10 ns, with wavelengths of 1064 or 532 nm [6][7][8][9][10]. The CR model has seen further use in investigating LPPs through the three-body and radiative recombination rate coefficients [9]; and it has also been extended, for example into a time-dependent version taking into account photoionization [10].…”

“…Typically in these experiments laser pulse lengths are on the order of 10 ns, with wavelengths of 1064 or 532 nm [6][7][8][9][10]. The CR model has seen further use in investigating LPPs through the three-body and radiative recombination rate coefficients [9]; and it has also been extended, for example into a time-dependent version taking into account photoionization [10]. Su et al investigated the evolution of Al (Z A = 13) LPPs and, as might be expected, determined that the impact of photoionization on the charge state distribution was more important for plasmas with lower electron densities in which relative collisional ionization rates are lower [10].…”

“…The CR model has seen further use in investigating LPPs through the three-body and radiative recombination rate coefficients [9]; and it has also been extended, for example into a time-dependent version taking into account photoionization [10]. Su et al investigated the evolution of Al (Z A = 13) LPPs and, as might be expected, determined that the impact of photoionization on the charge state distribution was more important for plasmas with lower electron densities in which relative collisional ionization rates are lower [10]. The photoionization rates reported by Su et al for Al 3+ to Al 6+ have orders of magnitude in the same range as the other rate coefficients.…”