Key Technology Research Band Interferometer

With the development of the high power laser and space optical system, surface quality of the optical components is required more and more highly and mid-frequency surface error evaluation is widely concerned. However, traditional evaluation methods of the optical components cannot meet the requirement. At present, there are few interferometers which can measure mid-frequency errors, bringing difficulties for optical components processing. In this paper, the key techniques of mid-frequency measurement have been studied and a high resolution interferometer has been designed.We analyze the different measurements and evaluation methods of surface error in different frequency range. The definition and computational methods of the power spectral density (PSD) which can be applied to evaluate the mid-frequency surface error are studied deeply. In addition, the relationship between the measured frequency range and sampling density in the calculation of the PSD is analyzed, and the PSD effective bandwidth of an interferometer is discussed.According to the theory of interferometry, the Φ15high resolution interferometer is designed to measure mid-frequency error. Besides, coherent noise caused by polarization beam splitter, collimating lens and the protective glass of CCD in the PSD interferometer is analyzed. We have finished assembling the interferometer and testing.The definition of transfer function in an interferometer is studied. The phase step is used to measure the system transfer function of the PSD interferometer. The experiments show that the system transfer function is0.75at the spatial frequency8.3mm-1, which meets the design requirement for measuring mid-frequency errors.