Research On The Testing Method Of Instrument Transfer Function Of An Interferometer

With the development of modern optical technique, it is necessary that the optics, especially in high accuracy optical system such as extreme ultraviolet lithography (EUVL) and inertia confinement system, need to be satisfied high accuracy in all frequency bands, in order to develop the high-accuracy optical quality. Interferometer is a kind of widely used instrument for measuring form errors of precision surface in modern optical testing. The instrument transfer function(ITF) is one of the most significant characters of an interferometer, as it could express the spatial frequency responds of an interferometer. In this paper, the survey on the testing method of ITF based on the ITF principle is developed, do the experiences with both power spatial density (PSD) and step comparison methods to obtain ITF, describe the effect of defocus, lateral resolution of the CCD camera and the step height on the ITF testing. The main contents are concluded as follows:1. Establish the modeling of ITF. Establish the mathematical analysis of ITF based on the scalar diffraction theory, in order to form the analysis the ITF testing theory foundation.2. Establish the testing method of ITF. State principle and computing method of power spatial density (PSD), introduce the both ITF testing methods of PSD and step comparison.3. Test the ITF. Devoted to doing the research on ITF testing with both two methods, and finally obtain the results. Compared results with these two methods, and the results show that the D-value of both method is less than4%within1lp/mm band.4. Describe the effects on the ITF testing. The height of the step of the standard testing plate should be well known in the ITF computing process, the height of the standard is well calibrated, and analyse the influence of the height of the step on ITF testing. Analyse the influence of the different defocuses and CCD resolution on ITF.