The principle of the free-vortex aerodynamic window (FADW) is described. The sealing property and influence of a FADW device designed for the 10 kW CO2 gas dynamic laser (GDL) on the optical quality have been studied experimentally. The experimental results show that this FADW device can attain a high sealing-pressure ratio PR>20, with the highest being 28 under the designing conditions, and that the FADW has a good starting-property and little influence on the optical quality. So this kind of free-vortex aerodynamic window is a promising alternative to take the place of the crystal windows.