Abstract: On optical element, such as a mirror, for example, has an optically polished surface which is neither planar or a section of surface of revolution. According to the invention, a flat member is machined along a second face so that the thickness of the flat member varies. The first face is optically polished when it is planar. The flat member is then distorted so that the surface is neither planar nor a section of surface of revolution. Such mirrors are used for distributing laser beam energy along lines or over extended areas with constant energy density.