Abstract
It is shown that defocusing in plasma layers and filaments results in reduction of the intensity, which can be compensated by amplification in a plasma medium. Defocusing increases somewhat the amplification threshold of a plasma layer or filament, but when this threshold is exceeded, the process of defocusing optimized in respect of its magnitude plays a positive role giving rise to single-mode emission, providing an opportunity for distributed coupling of energy out of a layer, and lifting limitations on the length of the active medium.