Patent ID: 8101930

Claim:
A method of increasing operational lifetime of an optical collector unit arranged in an irradiation device, said irradiation device comprising a radiation source for emitting extreme ultraviolet radiation or soft X-rays, said radiation source generating substances and/or particles colliding with optical surfaces of said optical collector unit, said optical collector unit forming a radiation beam of a portion of said radiation emitted by said radiation source, and a debris mitigation unit reducing an amount of said substances and/or particles which collide with optical surfaces of the collector unit, the method comprising: moving said optical collector unit such that deposits or degradation effects caused by collision of said substances and/or particles with said optical surfaces of the collector unit are distributed more homogeneously on said optical surfaces than without such a movement, wherein said collector unit is moved dependent on at least one of (i) measurement data of at least one optical sensor arranged to measure a light intensity or a light distribution of said radiation beam, (ii) operation time, (iii) operation voltage, and (iv) operation frequency.