Precision Interferometric Characterization to Accurately Test Aspheric Surfaces

Interferometric surface testing of optical components such as spheres and flats can be performed quite routinely with conventional interferometry where high accuracy can be achieved by incorporating reference subtraction or more complicated absolute characterization techniques. Aspheric null lens tests suffer from an inability to use reference subtraction or absolute calibration techniques to separate rotationally symmetric aberrations that exist between the test setup and the aspheric surface. Furthermore, zonal positioning errors that exist when imaging from surface to camera can be accounted for with conventional tests, but the zonal location of irregularities is crucial in the correction of aspheric components during the fabrication process. The interferometric null test bench must be designed, built, and characterized with high precision to achieve accurate aspheric surfaces.