Patent Number: 
Section: claims

1. An optical system, comprising:an illumination system having:a field plane in which a mask is located;a conjugated plane, conjugated to said field plane, and having a field stop situated therein, wherein said conjugated plane is situated in a light path from a light source to said field plane, before said field plane, so that light from said light source traverses through said conjugated plane;a first optical element having a first raster element in said light path before said conjugated plane;a second optical element having a second raster element in said light path after said first optical element; andat least a first mirror, in said light path, after said conjugated plane, for imaging a field in said conjugated plane into an image in said field plane. 2. The illumination system of claim 1, further comprising:a second mirror for imaging said field into said image, wherein light rays travel along a light path from said conjugated plane to said field plane; andan arc-shaped field in said field plane, whereby said arc-shaped field has a radial direction in a middle of said arc-shaped field defining a scanning direction,wherein said first mirror and said second mirror are arranged in said light path in such a position and having such a shape, that an edge sharpness of said arc-shaped field is smaller than 5 mm in said scanning direction,wherein said light rays are impinging on said first mirror and said second mirror with incidence angles less than or equal to 30° or greater than or equal to 60° relative to a surface normal of said first mirror and second mirror. 3. The illumination system according to claim 2, wherein said edge sharpness is smaller than 2 mm. 4. The illumination system according to claim 2, wherein the edge sharpness is smaller than 1 mm. 5. The illumination system according to claim 2, wherein said incidence angles relative to said surface normal are ≦20° or ≧70°. 6. The illumination system according to claim 2, wherein said illumination system includes an object field, and wherein said object field is arc-shaped. 7. The illumination system according to claim 2, wherein said first mirror and said second mirror are part of an imaging system and the imaging system has a magnification ratio unequal to 1. 8. The illumination system according to claim 7, wherein said imaging system is a non-centered system. 9. The illumination system according to claim 2, wherein said first mirror and said second mirror are part of an imaging system and said imaging system comprises an exit pupil and an aperture stop that is located on or close to a plane conjugated to said exit pupil. 10. The illumination system according to claim 2, wherein said first mirror and said second mirror are part of an imaging system, said imaging system comprises an exit pupil, and said first mirror is positioned close to a plane conjugated to the exit pupil. 11. The illumination system according to claim 2, wherein said first mirror and said second mirror are aspheric mirrors. 12. The illumination system according to claim 2, wherein said first mirror is a concave mirror having a nearly hyperbolic form or a nearly elliptic form, and wherein said first mirror defines a first axis of rotation. 13. The illumination system according to claim 12, wherein said second mirror is a concave mirror having a nearly hyperbolic form or a nearly elliptic form, and wherein said second mirror defines a second axis of rotation. 14. The illumination system according to claim 13,wherein said first axis of rotation and said second axis of rotation subtend to an angle γ, andwherein said first mirror and said second mirror define a first magnification for a chief array traveling through a center of said field and a center of an exit pupil, a second magnification for an upper COMA ray traveling through said center of the field and an upper edge of said exit pupil and a third magnification for a lower COMA ray traveling through said center of the field and a lower edge of said exit pupil,whereby the angle γ between said first axis of rotation and said second axis of rotation is chosen so that said first, said second and said third magnification is nearly identical. 15. The illumination system according to claim 2, wherein said first mirror and said second mirror have a used area, and wherein said used area is arranged off-axis with an axis of rotation of said first mirror and said second mirror. 16. The illumination system of claim 2, wherein at least one of said first mirror or said second is an aspheric mirror. 17. The illumination system according to claim 1, further comprising a field-forming optical component in said light path, after said conjugated plane, that shapes said image. 18. The illumination system according to claim 1, further comprising a field-forming optical component in said light path, before said conjugated plane, that forms said field. 19. The illumination system according to claim 17, wherein said field forming optical component is situated in a light path from the light source to said field plane downstream from said conjugated plane to said field plane. 20. The illumination system according to claim 1, wherein said first mirror is part of a multi-mirror system. 21. The illumination system according to claim 1, wherein said first raster element is a field facet and said second raster element is a pupil facet for directing said light from said light source to said conjugated plane. 22. An EUV-projection exposure unit for microlithography, comprising:the illumination system according to claim 1, wherein said mask is arranged on a carrier system in said field plane; anda projection objective for imaging said mask onto a light-sensitive object on a carrier system. 23. The EUV-projection exposure unit according to claim 22, wherein the unit is designed as a scanning system. 24. A process for producing microelectronic devices with the EUV-projection exposure unit according to claim 23. 25. The illumination system of claim 1, wherein said source emits light having a wavelength of less than or equal to 193 nm.