This paper describes the design and experiments of three types of aerodynamicwindows——expansion window, compression window and vortex window. Three windows have anaperture of 3 cm and were designed to operate at a cavity pressure of 0.1 atm. While the beam passes through the window, the minimum beam degradation is 1.5 times as large as the diffraction limit of the aperture. The minimum mass flow required for the operation of the window is 0.012 kg/sec.cm2.