An apparatus for substrate treatment by means of laser radiation includes a rotating polygonal mirror by which at least one incident laser beam is reflected and is pivotable across an arrangement of converging lenses which lie next to one another and which are arranged at a spacing from the substrate corresponding precisely or approximately to their focal lengths. The rotating polygonal mirror is divided into at least two regions having a different number of facets and is adjustable such that different regions can be introduced into the beam path of the laser radiation and accordingly different sweep angles or fan angles of the laser beam reflected by the rotating polygonal mirror can be set.