Patent ID: 7196842

Claim:
An attenuating filter comprising: a substrate fabricated from a material which is transparent to ultraviolet light; and at least one filter coating applied to a surface of the substrate; the filter coating comprising at least one layer fabricated from an absorbing dielectric material that absorbs over a predefined wavelength range; wherein the thickness, measured perpendicular to the surface of the substrate, of the layer of absorbing dielectric material of the filter coating varies smoothly over the surface of the attenuating filter, wherein the variation in the thickness of the layer of absorbing dielectric material causes a spatial variation of the transmittance of the filter coating across the surface of the attenuating filter, and thereby provides a prescribed attenuation of the intensity of transmitted ultraviolet light over a predefined wavelength range according to a predefined spatial distribution of spectral transmittance; and wherein the filter coating has a maximum thickness of less than 10 nm.