Testing of aspheric surfaces

Aspheric surfaces are becoming interesting for the reduction of elements in optical systems as well as for improving the quality of the image forming system. The fabrication process of aspheric surfaces has been improved. For optical testing of aspheric surfaces computer generated holograms (CGHs) are interesting and already used. To perform aspheric testing in the same accuracy as spherical surface testing, further improvements of the CGH-null test method are required. A new concept for testing aspheric surfaces with CGH-nulls, including a calibration of the system, will be described. To specify and verify CGH quality, systematic errors due to fabrication inaccuracies of the CGHs will be analysed. On the other hand, alternative methods that provide more flexibility but possibly less accuracy than the CGH-null technique are required. Potential alternative testing methods of aspherics will be discussed.