Quasi-absolute interferometric test for Toroidal surfaces by using Combined Diffractive Optical Elements

The industrial demand for toric surfaces has increased because of their use in astigmatic systems like laser scanning devices and electronic printers. Testing of these surfaces in an absolute manner is more complicated than that of flats, spheres or even rotationally symmetric aspherics because of the reduced degree of symmetry. By utilizing the orthogonality of the two axes of principal curvatures, we propose a quasi-absolute three position procedure for their absolute measurement. These three positions are: the basic position (0°), the rotated position (180°) and the cat’s eye position. A combined diffractive optical element has been employed to generate the toroidal as well as spherical wavefront simultaneously. The toroidal wavefront was used for the first two measurements. The third measurement, the cat’s eye position, has been captured by a spherical wavefront.