Fundamental studies on direct conversion from thermalenergy to photo energy using unsfeady exciled state ofmolecales

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This study was done in order to develop CO_2 gas dynamic laser using unsteady states generated by combustion of hydrocarbons as a converter of thermal energy to photo energy An unsteady flame propagation combustor was developed applicable to the driving gas generator. In this study, the fundamental characteristics of the combustor using methane/air at normal pressure and pressurized condition were experimentally investigated. It was found that the combustor has the wide turn-down ratio up to 48 digit. It means the combustor can be controlled in the wide load. The combustion of methane/air was well promoted because combustion is occurred through the whole combustion chamber.The effect of coexisting H_2O with high concentration on the population balance between CO_2 (001) and CO_2 (100) levels was theoretically investigated. It was found that the populations inversion between their levels enough to obtain laser emission can be realized when the combustion gas with the methane/air at stoichiometric ratio is adiabatically expanded so as to achieve the Mach number 5.0 through the supersonic nozzle. The ratio of the number densities becomes maximum at 0.4 of H_2O in concentration, and the location where the peak appears shifts upstream with increasing H_2O concentration. The magnitude of the population inversion increases with increasing C/H of fuel in constant concentration of N_2. But the width in the streamline keeping the population inversion becomes narrow in high concentration of H_2O.Based on the experimental and theoretical studies above, the gain measurements to confirm an existence of a population inversion were done. The results obtained showed that input laser power was amplified through a laser cavity. It meant the appearance of the population inversion.