Theory of porous wall capillary tubes for flowing gas lasers

Flowing gas capillary lasers exhibit high optical gains. However, as a result of the linear axial pressure variation in the tube bore, gain and saturation intensities are not axially uniform. This pressure variation can be reduced by introducing the gas into the tube bore through the walls of a porous capillary tube. Analysis of the gas flow shows that the axial pressure variation in the porous wall tubes is more gradual than for dense wall tubes leading to more uniform gain conditions. The saturation intensity is more uniform not only due to the reduced pressure anisotropy but also, at higher flow rates, because of axially varying particle dwell times in the discharge region.