a pair of cooling members, each including an extended surface, opposed such as to form a light guide for propagation of optical radiation in the gap between said surfaces;

a laser gas, disposed in said gap to generate laser radiation via excitation of said gas by an electric discharge provided by high-frequency electric power supplied to said gas,

mirrors, forming a traveling wave ring resonator with a closed axial contour to generate a laser beam in aid light guide,

wherein:

said mirrors are disposed such that said axial contour of said resonator lies essentially in the plane, which is located between said surfaces of said cooling members forming said light guide for optical radiation and faces with its opposite sides said surfaces of said cooling members, said traveling wave ring resonator being unstable in said plane so that part of said beam expanding in said resonator is coupled out of the laser as an output beam of solid cross-section, the number of said mirrors and their curvatures being such that any ray belonging to said beam and propagating along said light guide inside said axial contour of the resonator emerges after a round trip to propagate outside of said axial contour, and any ray belonging to said beam and propagating along said light guide outside of said axial contour of the resonator emerges after a round trip to propagate inside said axial contour.