Optical assembly for guiding an output beam of a free-electron laser

摘要

An optical assembly (13) serves to guide an output beam (2a) of a free-electron laser (FEL, 2) towards a downstream illumination optical assembly (15) of an EUV projection exposure apparatus. The optical assembly (13) has a first and a second GI mirror (23, 25), each with a structured reflection surface (24, 26) for application to the output beam (2a). A first angle of incidence (α) on the first GI mirror (23) is greater than 1 mrad and less than 10 mrad. A maximum first scattering angle of at least 50% and at most 100% of the first angle of incidence (α) is produced. A second angle of incidence (α) on the second GI mirror (25) is at least twice as large as the first angle of incidence (α). A maximum second scattering angle of the output beam (2a) is at least 30% and at most 100% of the second incident angle (α). The two planes of incidence (yz, xy) on the two GI mirrors (23, 25) enclose an angle to each other which is greater than 45 °. The result is an optical assembly with which an output beam of a FEL can be performed safely and with sufficient life of the optical components. A hollow waveguide assembly with two electrodes and an ionization light source may be part of such an optical assembly (13). A magnet arrangement with at least one magnet-pole pair can also be part of such an optical assembly (13).