Patent ID: 7593095

Claim:
A system for reducing the coherence of a wavefront-emitting laser radiation for a projection objective in semiconductor lithography, a first partial beam of the laser beam impinging on a surface of a resonator body being partially reflected and a second partial beam of said laser beam entering the resonator body and emerging from the resonator body again after a plurality of total reflections at least approximately in the region of the entrance location and being forwarded with the first partial beam jointly to an illumination plane, the resonator body being formed in such a way that in addition to the splitting into partial beams, the wavefronts and at least one partial beam are modulated during a laser pulse, the partial beams which are reflected at the resonator body and which enter the resonator body being superimposed downstream of the resonator body, and the resonator body being provided with a phase plate having varying local phase distribution, wherein the phase plate has different thicknesses for the passage of the second partial beam of the laser beam transversely with respect to the beam direction, the different thicknesses of the phase plate varying in the transverse direction in a width s; and wherein the variations in the width s are of the order of magnitude of the spatial coherence length of the laser radiation at the entrance plane.