Patent ID: 7050237

Claim:
A method for spectrally purifying light, comprising: providing a multilayer comprising at least 2 thousand periods, wherein said multilayer has been deposited onto a mirror substrate, wherein said multilayer is cut and polished at a cut angle to produce an asymmetrically cut surface such that desired EUV light having wavelengths only within a range from 11–14 nm directed onto said asymmetrically cut surface will be Bragg diffracted by said multilayer and undesired light having wavelengths only outside of said range will be absorbed in said multilayer or reflected by said asymmetrically cut surface; providing source light comprising a spectrum that includes said desired EUV light and said undesired light; and directing said source light onto said asymmetrically cut surface at an incidence angle such that only said EUV light Bragg-diffracts from said multilayer.