Numerical analysis of thermal defocusing in a pulsed CO2 amplifier

A numerical analysis is made of the dependence of thermal defocusing of the output beam in a CO₂ amplifier on the parameters of the input radiation pulse. It is found that defocusing is appreciable when the pulse duration is comparable with the time needed for equalization of the gas pressure over the cross section of the beam. The Hamiltonian formalism is used to describe the quality of the output beam. It is shown that wavefront reversal of the beam can be used to suppress this type of defocusing in amplifiers.