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An elliptically bent mirror of total length 1.25 m has been developed at the Advanced Light Source (ALS) for focusing soft x-rays. The mirror is used to produce a small, high flux density illuminated field of view for a Photo-Emission Electron Microscope. The requirement to collect the maximum horizontal aperture with the need to highly demagnify the source leads to a mirror with a wide range of curvatures along the surface. This combined with the need to produce a low slope error surface at a reasonably low cost has required us to develop a mirror based on the controlled bending of a flat substrate. This is an extension of several other mirror projects at the ALS where controlled bending of glass and metal substrates has been used in micro-focusing applications. Those mirrors however are a maximum of 200 mm long, and in this paper we describe the new challenges we have faced and the solutions we have adopted in developing a long and highly elliptical mirror. The mirror described here is manufactured from a low carbon steel (1006) which is capable of good dimensional stability, it is electroless nickel plated for polishing, and is bent into an elliptical shape by the application of unequal couples. We describe the mirror fabrication process, the mechanical details of the bending mechanism and the experimentally measured slope error from an ellipse. The final mirror has an rms roughness of 6 angstroms (rms), a full aperture (1.1 m) slope error of 14 (mu) rad (rms), and a slope error of < 3 (mu) rad when optimized over approximately 2/3 of the required optical length (0.917 m).
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