Abstract: The invention relates to an optical system with a dividing element (2), which divides the input laser beam (EL) into a number of spatially separate sub-beams, at least one optical amplifier (4), through which the spatially separate sub-beams propagate, at least one path-length adjustment element (3), which adjusts the path length of at least one of the sub-beams, and a combination element (6, 8), which coherently superimposes the sub-beams in an output laser beam. The object of the invention is to achieve a high beam quality in the output laser beam, wherein the demands on the surface quality of the optical components used are to be reduced compared with the prior art.