Simulation of multimode lasing in an electron-beam-controlled CO2 laser with an unstable cavity under thermal self-action of radiation

A numerical technique for calculating the time-dependent multimode lasing in an electron-beam-controlled CO₂ laser at significant optical inhomogeneities caused by radiation self-action is presented. The reported calculations for subatmospheric pressure yield a sequence of involvement of transverse modes in lasing, the evolution of their characteristics (which is self-consistent with the evolution of gain and optical inhomogeneities of the active medium), and the exclusion of output modes from lasing. This calculation technique can be used when the radiation round-trip time around the cavity is shorter than the characteristic time of change in the active-medium characteristics.