Topological phase defects in radiation of technological CO2 lasers with stable and unstable resonators

Phase characteristics of the output beam of periodic-pulse CO₂ lasers with long stable and unstable resonators are discussed. Wavefront diagnostics of each pulse of the train is performed by shearing interferometry methods. Attention is focused on the most general topological properties of the phase surface. It is established that the wavefront topology varies from pulse to pulse, remaining equivalent to the simplest distorted sphere characteristic of the initial pulses of the train. The observed distortions and their spatial density are localized randomly over the cross section of the laser beam. The topological transformations are shown to be caused by thermal distortions of the resonator mirrors and other processes producing inhomogeneities in the laser resonator. It is suggested that the wave distortions are typical defects of high-power lasers of all types.