| CPC G02B 5/0891 (2013.01) [G02B 5/09 (2013.01); G02B 19/0095 (2013.01); G03F 7/70316 (2013.01)] | 12 Claims |

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1. Collector mirror configured for extreme ultraviolet (EUV) light, comprising:
a reflection surface to reflect usable EUV light which impinges on the reflection surface from a source region to a subsequent EUV optics,
wherein the reflection surface carries a pump light grating structure configured to retroreflect pump light which impinges upon the pump light grating structure from the source region back to the source region, the pump light having a wavelength (λPL) deviating from the wavelength of the usable EUV light, and
wherein a pitch of the pump light grating structure varies over the reflection surface of the EUV collector mirror.
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