Nowadays, a chemical laser has been developed not only for a strategic military purpose, but also as a manufacturing tool in industrial usage due to its high power lasing characteristics. In order to increase the laser beam power in the chemical laser systems, the mixing efficiency of fuel and oxidant should be improved, since more excited molecules are followed by high mixing efficiency. Basically, the production of a lot of excited molecules in the laser cavity results from the high mass flow rates of fuel and oxidant based on efficient mixing and chemical reaction. Therefore, in order to supply higher mass flow to the chemical laser cavity, a radial-expansion nozzle array was used and examined here, not a planar nozzle array which has been widely employed until now. The laser beam generation in this system is achieved by mixing F atoms from supersonic nozzle with D-2 molecules ejecting from holes of round-bended supply lines which are distributed in zigzag configuration, which would extend the reaction zone. Consequently, more excited molecules are expected to be produced, so the intensity of population inversion will be higher. Since the two-stream injection angle was considered to influence the performance of supersonic combustor, the effects of D2 injection angles against the main F flow on mixing enhancement, population inversion and gain characteristics were numerically investigated in this study. The results were discussed by comparison with three cases of D2 injection angles such as 10 degrees, 20 degrees and 40 degrees against the main flow direction. As the injection angle increases, two counter-balancing effects were observed. (C) 2007 Elsevier Ltd. All rights reserved.