Time Resolved Luminescence Spectroscopic Analysis in Plasma Switching by Laser Ablation of the Gaseous Cu-CF 4 System

Abstract

Plasma switching by laser ablation (PLASLA) is the phenomenon that, in a lower electric field, laser ablation forms the pulse plasma whose on-off timing completely synchronizes with the laser ablation, discovered by us in the gaseous reaction system of laser ablated Cu and CF4 and considered promising for materials science, as reported previously. Here we study the chemical processes of PLASLA by measuring the time-resolved luminescence spectra as well as the dc-plasma luminescence spectra. It is found that the PLASLA spectrum at 0.5 s after the laser ablation is quite different from the spectra at 8 s and 0.25 ms, which are found to be essentially the same as the CuF chemiluminescence spectrum of the gaseous reaction of CF4 with laser ablated Cu, suggesting that PLASLA has the specific initial processes and the reaction system changes toward the one rather similar to the chemiluminescent reaction system. The analysis of the complicated spectrum at 0.5 s finds that it is composed of the bands assigned to C, C+, C2+, C2, CuF, Cu, Cu2, N2, and N2+, suggesting that the product materials of PLASLA are carbon polymers, which agrees with the conclusion from our previous time-of-flight mass spectrometric study. The fact that the CuF luminescence is due to only the singlet states at 0.5 s and both the singlet and triplet states at 8 s and 0.25 ms significantly indicates that CuF is formed by Cu+ and CF4 through only the singlet-spin-states reaction coordinates at 0.5 s by keeping the strict spin conservation, which is broken by the relaxation processes after that. The fact that the spin conservation like this is broken through the spin-states mixing by a magnetic field has already been reported by our previous paper on the CuF-chemiluminescence reaction of CF4 with laser ablated Cu.