Abstract
Laser-induced ignition by ArF excimer laser was investigated and the ignition pattern and minimum ignition energy in a CH_4-air mixture were determined. In the case of the minimum focused ignition energy, the tendency for the minimum oxygen dissociation ratio for ignition to change with temperature disagreed with the results of chemical reaction kinetics simulation analysis. This led to the conclusion that the mechanism of focused ignition may be different from that of the photodissociation process. To clarify the ignition mechanism in detail, research was carried out on the partial saturation of the laser spectrum and oxygen molecular depopulation at high vibrational levels in lower states during laser emission. The results agreed with the analytical results for a model without vibrational relaxation in terms of the line-shaped ignition photodissociation condition, but the temperature-related tendency of the minimum oxygen dissociation ratio for ignition clearly disagreed with that obtained by the analysis of chemical reaction kinetics simulation. This imposes the need for reconsideration of the mechanism of focused ignition.
