Fine-structure in the transverse mode of an excimer laser beam is minimized by having a plurality of resonator mirrors located at each end of a linear excimer laser. At one end, a highly-reflective end mirror and a partially-reflective end mirror are inclined at small angle with respect to each other. At the other end, two output-coupling mirrors are inclined at a small angle with respect to each other. This arrangement of resonator mirrors generates a composite laser beam that blurs any fine structure.