Testing optical aspheric surfaces by aspherics characteristic interferogram

The interference pattern of the optical path difference between an aspherical optical surface and the corresponding best fit spherical surface is the Aspherics Characteristic Interferogram (ACI), which can be used as a template to test aspheric optical surfaces without test plates or null compensation systems. This direct interferometry can be used in the optical shop testing & in the digital phase-shifting spherical Fizeau interferometer to achieve high precise aspheric surface testing automatically. We succeeded in testing several aspheric surfaces by this method. ACI is also the base of phasing segmented mirrors, and six small-segmented mirrors were successfully combinated to a large minor. If used in the infrared red interferometer, strongly aspheric surfaces with asphericity more than 40 mum can also be tested. Experiments show that the ACI is a fast, effective aspherical surface measurement technique.