An EUV mask inspection system, comprising: a light source projecting EUV light along an optical axis; an illumination system receiving the EUV light from the light source, the illumination system comprising a spectral purity filter (222, 322, 422), a relay, a homogenizer and a condenser, the spectral purity filter (222, 322, 422) transmitting a first portion of the EUV light along the optical axis toward a mask and the spectral purity filter (222, 322, 422) comprising a plurality of mirror surfaces reflecting a second portion of the EUV light off the optical axis, wherein the spectral purity filter (222, 322, 422) is located proximate the end of the homogenizer, the spectral purity filter (222, 322, 422) defined by a first axis (x) and, a second axis (y), the first axis (x), second axis (y) and optical axis being mutually perpendicular to one another, the spectral purity filter (222, 322, 422) comprising: a two dimensional array of channels disposed in a plane defined by the first axis (x) and the second axis (y), each channel defined in the direction of the first axis (x) by an upper side and a lower side, and defined in the direction of the second axis (y) by, a right side, a left side, each channel extending in the direction of the optical axis and a same one of said upper side, right side, left side and lower side, for each channel, having a mirror surface of the plurality of mirror surfaces attached thereto, and each mirror surface is disposed at an angle relative to said one of said upper side, lower side, right side and left side, such that the mirror surfaces at least partially face a proximal end of the spectral purity filter (222, 322, 422) along the optical axis of the spectral purity filter (222, 322, 422), and a thin film filter disposed to cover each channel at the proximal end of the spectral purity filter (222, 322, 422); a projection system receiving the first portion of the EUV light after it has illuminated the mask and thereby form an image of the mask; a first detector array receiving the image of the mask; and a second detector array receiving the second portion of the EUV light. a light source projecting EUV light along an optical axis; an illumination system receiving the EUV light from the light source, the illumination system comprising a spectral purity filter (222, 322, 422), a relay, a homogenizer and a condenser, the spectral purity filter (222, 322, 422) transmitting a first portion of the EUV light along the optical axis toward a mask and the spectral purity filter (222, 322, 422) comprising a plurality of mirror surfaces reflecting a second portion of the EUV light off the optical axis, wherein the spectral purity filter (222, 322, 422) is located proximate the end of the homogenizer, the spectral purity filter (222, 322, 422) defined by a first axis (x) and, a second axis (y), the first axis (x), second axis (y) and optical axis being mutually perpendicular to one another, the spectral purity filter (222, 322, 422) comprising: a two dimensional array of channels disposed in a plane defined by the first axis (x) and the second axis (y), each channel defined in the direction of the first axis (x) by an upper side and a lower side, and defined in the direction of the second axis (y) by, a right side, a left side, each channel extending in the direction of the optical axis and a same one of said upper side, right side, left side and lower side, for each channel, having a mirror surface of the plurality of mirror surfaces attached thereto, and each mirror surface is disposed at an angle relative to said one of said upper side, lower side, right side and left side, such that the mirror surfaces at least partially face a proximal end of the spectral purity filter (222, 322, 422) along the optical axis of the spectral purity filter (222, 322, 422), and a thin film filter disposed to cover each channel at the proximal end of the spectral purity filter (222, 322, 422); a projection system receiving the first portion of the EUV light after it has illuminated the mask and thereby form an image of the mask; a first detector array receiving the image of the mask; and a second detector array receiving the second portion of the EUV light. a two dimensional array of channels disposed in a plane defined by the first axis (x) and the second axis (y), each channel defined in the direction of the first axis (x) by an upper side and a lower side, and defined in the direction of the second axis (y) by, a right side, a left side, each channel extending in the direction of the optical axis and a same one of said upper side, right side, left side and lower side, for each channel, having a mirror surface of the plurality of mirror surfaces attached thereto, and each mirror surface is disposed at an angle relative to said one of said upper side, lower side, right side and left side, such that the mirror surfaces at least partially face a proximal end of the spectral purity filter (222, 322, 422) along the optical axis of the spectral purity filter (222, 322, 422), and a thin film filter disposed to cover each channel at the proximal end of the spectral purity filter (222, 322, 422); a projection system receiving the first portion of the EUV light after it has illuminated the mask and thereby form an image of the mask; a first detector array receiving the image of the mask; and a second detector array receiving the second portion of the EUV light.