Self-interaction of radiation in a CO2 laser resonator

A theoretical investigation is made of the self-interaction of radiation in a CO₂ laser resonator allowing for the diffraction at the mirrors. It is shown that the influence of the thermal nonlinearity of the active medium on the spatial mode structure depends strongly on the Fresnel number of an unstable resonator and it may result in a strong deformation of the output radiation modes. The nature of this deformation is governed largely by the transient nature of gasdynamic perturbations and by the inertia of the thermal nonlinearity mechanism.