Formation of excited states of atoms and ions in laser plasma from CuInS2

Abstract

Emission spectra and the energy distribution of the excited-state population density of atoms and ions in erosion laser plasma from CuInS2 with various crystal-structure orderings are analyzed. It is shown that increased ordering of the target crystal structure causes the excited-state energies of indium atoms generated in the laser erosion plume to increase and that sulfur atoms always emit only in transitions from highly excited states. The ratio of relative ion concentrations in the laser plasma plume is Cu+/In+/S+ = 0.3/0.08/2, which corresponds neither to the atomic ratio of Cu/In/S (1/1/2) in the target nor to the ratio of ionization energies. The results are explained by recombination processes for ions and by the atomization specifics of the CuInS2 target exposed to long-wavelength radiation. The atomization consists essentially of dissociative processes expressed by CuInS2 → CuInS + S and CuInS2 → Cu + InS + S. The electron temperature of polycrystal (single-crystal) plasma at a distance of 1 mm from the target is 0.3 eV (0.4 eV) for atoms and 1.3 eV (2.7 eV) for ions and varies negligibly for plasma up to a distance of 7 mm from the target.