Two Computer-generated Holograms For Testing Convex Aspheric Surface

Three hundred years ago, since Newton used a parabolic reflector to replaceunachromatic lens for the first time, aspheric surface has been applied more and more invarious optical systems. Compared to spherical surface, aspherics can greatly improve theperformance of optical system, including image quality, miniaturization and lightweight.With the rapid development of space sense technology and advanced optical instruments,large aperture and high precision optical surface has been widely used. However,applications of aspherics have been limited by optical manufacture and testing technologyfor a long time. Although the current machining technology has been developed rapidly,the level of testing is relatively out of date, and as a whole, is not able to satisfy theapplication requirement timely. There are many methods in the testing of aspheric surface,but they have limitation respectively.Aim to the problem on convex aspherical measurement with high precision, this paperdiscusses a new method for testing convex aspheric surface——two CGHs, the mainresearch we did is as follows:1. Some general methods for testing convex aspheric surface were introduced; theprevious design and development of testing aspheric surface with CGH weresummarized. All these laid a foundation for the follow-up research.2. The principle of testing convex aspherics with two CGHs was analyzed, the overalldesign principle of system and each component was determined. For an actual convexhyperboloid mirror, a testing system was designed and optimized in Zemax. In addition,using this method to test free-form surface was discussed.3. System errors were analyzed in detail by using the error theory, including the manufacture errors, assembly and adjustment errors of the components. These errorsshould be controlled to improve the accuracy in actual testing.4. Based on the principle that superposition of two proximity gratings with closefrequencies can produce moiré fringes, a method of fabricating four pairs of circulargrating around the main CGH was proposed in order to align CGH componentsprecisely. The principle of moiré fringes was expatiated, the results were simulatedtheoretically and the feasibility was confirmed by an experiment.