Computer-generated holograms in interferometric testing

Computer-generated holograms (CGH) are on their way to becoming a state-of-the-art component in interferometry. We give an overview on recent developments in calibration and testing of aspheric surfaces with CGH. The starting point is a new absolute calibration method for binary Fresnel zone mirrors (FZM) that allows separation of the errors introduced by the imperfectly written FZM pattern from the errors of the substrate and from the interferometer errors. This leads to a variety of applications for FZM, ranging from absolutely calibrated spherical master surfaces to quality control of CGH fabrication. We then focus on a major application of binary CGH: null tests for testing of aspheric surfaces. Useful test setups are described and an alignment strategy utilizing auxiliary structures in the periphery of the CGH is discussed. The section on binary CGH culminates with the first absolute test method for measuring aspheric surfaces and systems. We close our overview with diffractive transmission spheres. Diffractive transmission spheres offer high accuracy of the generated wavefront, low weight, and new alignment possibilities with the help of flexible auxiliary structures. They are fabricated in a grayscale technique that provides high-efficiency blazed structures. Prototypes are shown and measurement results are given. (C) 2004 Society of Photo-Optical Instrumentation Engineers.