Abstract The multimode radiation of a high-power solid-state laser is dealt with as a Gaussian Schell model (GSM) beam that is described by the Wolf function. The laser beam parameters for a stable resonator configuration were calculated and compared with experimental results. The focusing of the GSM beam by means of a thin lens (first-order optical system) and the disturbance by an aperture diaphragm are discussed by means of two-dimensional graphics. For multimode radiation the advantage over ray-tracing methods are discussed.