Double Counting Hologram Used For The Aspheric Absolute Test Of The Study

Usually in the interferometric test of surface, the result contains the error of the interferometer and so on. And the absolute test can avoid the influence of the interferometer error. In the absolute test, the surface is tested sequentially for several times, and then the wavefront error is computered, so the error of the surface is tested absolutely, the precision of test got improved.First the basic properties of aspheric surface and the testing methods are described. The absolute test of aspheric surfaces is presented based on the difference between with spherical and the absolute test method of spherical surface. In the absolute test of aspheric surfaces, a Twin Computer-generated Holograms(Twin-CGH) is used. Then the encode methods and conditions of the Twin-CGH are discussed and the errors of the CGH is analyzed. In the Twin-CGH, if one of those is used for calibration by means of known absolute interferometric method, then the aberrations of the calibration wavefront can be transferred to those of the second wavefront. To prove this viewpoint, the encoded Twin-FZM is used and this novel calibration method is experimentally demonstrate and the compared result is excellent agreement.