The physical nature and manifestation of several types of instabilities and fluctuation processes in the cavity of the fast-flow CO2 -laser are considered. It was established by experiment that optimal design of optical and gas-dynamic laser sections depresses totally the high frequency fluctuations and reduces low-frequency fluctuations to the level 6-10%. It was shown that inhomogeneities in the laser cavity are apt to complicate appreciably the space-temporary structure of output laser radiation. To interpret the experimental results influence of phase aberrations on the process of formation of caustics and wavefront dislocations in laser beam is considered.

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Numerical simulations of self-pulsing oscillations in fast-flow laser fitted with unstable generator and multipass amplifier were performed. Possibility of the control of the depth of power modulation was shown. A number of governing parameters can be used to vary the regime of lasing in the system. Modulation of output power depending on the pumping rate was observed experimentally in fast-flow CO2 laser

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