Integrating Figure and Finish Measurements with Surface Profiling Instruments

Abstract

Conventional figure measurement techniques are inadequate for testing aspheres for grazing incidence applications. Conventional techniques are best suited for optical components in the shape of flats, spheres, or conical surfaces of revolution, used mainly in normal incidence applications . These optics usually have their symmetry axis coincident with the local surface normal direction. Grazing incidence optics, on the other hand, are usually cylindrical, toroidal, or ellipsoidal in shape, with the symmetry axis intersection far outside the clear aperture. Such surfaces are not axisymmetric when viewed along their surface normals. They are highly anamorphic, having vastly different curvatures in the two directions parallel and perpendicular to the symmetry axis. It is extremely challenging to test these optical components during fabrication to insure that they indeed meet the specifications for figure and finish quality. It is because of the extreme difficulties involved in developing reliable tests with conventional interferometric techniques that we decided to use profiling techniques to characterize the figure and finish of synchrotron radiation (SR) optics.