Machining of paraboloidal mirrors

Abstract

Paraboloidal mirror surfaces transform plane wavefronts into spherical ones and vice versa. This allows us to perform an interferometric measurement of its shape without the need of compensating optics or a CGH. From measurement's point of view there are good preconditions to manufacture high accuracy paraboloidal surfaces. On the other hand machining has to deal with the aspherical deviation to the best-fitting sphere. Depending on the amount of this deviation and the material of the mirror, different machining technologies are applied to bring the surface into paraboloidal shape. Off-axis paraboloids provide even more challenges in machining. There are two accepted approaches for manufacturing off-axis precision paraboloids. One way is to figure and polish a rotationally symmetric part with subsequent separating the off-axis elements from the parent paraboloid. On the other hand you can machine the single parts right from the start. In this case the surface is a kind of freeform. In this paper we discuss the manufacturing of on-axis and off-axis paraboloidal mirrors applying various methods.