Patent ID: 8390785

Claim:
A collector optical system in which radiation is collected from a radiation source and directed to an image focus, the collector optical system comprising: a source focus residing along an optical axis and at which the radiation source is located; two or more mirrors, each mirror being symmetric about the optical axis and having at least first and second reflective surfaces, wherein the first and second reflective surfaces having a common focus such that the radiation from the radiation source undergoes successive grazing incidence reflections at said first and second reflective surfaces and is focused at an intermediate focus that resides on the optical axis; and wherein the common focus is transversely offset by a predetermined distance Δr with respect to the optical axis so that an off-axis line through the intermediate focus and the common focus defines an angle α with respect to the optical axis that is in the range from about 1 milliradian (mrad) to about 100 mrad.