Emission spectroscopy of a carbon plasma formed by laser ablation of graphite. I. Ablation by XeCl laser radiation

The method of time-resolved emission spectroscopy was used to investigate the luminescence emitted by a carbon plasma plume formed as a result of vacuum ablation of graphite by XeCl laser radiation. It was found that in the course of emission from the plasma the spectrum of this luminescence changed drastically and, at laser radiation energy densities Φ = 4 — 5 J cm^–1, the main contribution came from the emission by C⁺ ions and C₂ radicals. The emission kinetics depended on the excitation conditions and it also varied from one part to another of the plasma plume. A method was developed for computer simulation of the spectra of C₂ radicals, which made it possible to determine the plasma vibrational and rotational temperatures (T_rot and T_vib) from the recorded luminescence spectra of these radicals, and also to study temporal evolution of these temperatures. During the emission time the characteristic temperatures of C₂ radicals were found to vary within wide limits: T_vib = 2500 — 12000 K, T _rot = 1500 — 10000  K.