Study of population inversion and laser beam generation in DF chemical laser system

Abstract

Nowadays a chemical laser is globally studied and examined as a means of new high strategic weapon system or industrial equipment system. Different from the other laser systems, the chemical laser system has a great advantage in that a high power laser beam with megawatt range can be easily generated. In order to do that, the chemical laser system employs a supersonic mixing and chemical reaction in the cavity. In the DF chemical laser system, F atom as an oxidant and $D_2$ molecule as a fuel are injected and reacted so that the DF excited molecules are produced. These phenomena occur in a non-equilibrium state. The excited molecules are degenerated into the lower level energy states so as to generate the laser beam by means of the stimulated emission. Therefore, more excited molecules in higher energy level are desirable in order to generate a higher power laser beam by controlling a flow mixing and chemical reaction in the cavity. There are a lot of factors that may affect mixing and chemical reaction in producing excited molecules. The $D_2$ injector pressure which controls the rate of $D_2$ supply, base which forms a recirculation zone to determine characteristics of mixing and chemical reaction, $D_2$ injection angle and so on can be considered. In the present study, these phenomena are investigated by means of analyzing the distributions of the DF excited molecules and the F atom used as an oxidant, while simultaneously estimating the maximum small signal and saturated gains and power in the DF chemical laser cavity. An 11-species (including DF molecules in various excited states of energies), 32-step chemistry model is adopted for the chemical reaction of the DF chemical laser system. Additionally, in order to overcome the difficulty for the planar nozzle array which has been widely used until now to supply high mass flow to the chemical laser cavity, a radial expansion nozzle array as an innovated alternative of the planar nozzle system is also numerica...