The swing arm profilometer (SAP) has been playing a very important role in testing large aspheric optics. As one of most significant error sources that affects the test accuracy, misalignment error leads to low-order errors such as aspherical aberrations and coma apart from power. In order to analyze the effect of misalignment errors, the relation between alignment parameters and test results of axisymmetric optics is presented. Analytical solutions of SAP system errors from tested mirror misalignment, arm length L deviation, tilt-angle θ deviation, air-table spin error, and air-table misalignment are derived, respectively; and misalignment tolerance is given to guide surface measurement. In addition, experiments on a 2-m diameter parabolic mirror are demonstrated to verify the model; according to the error budget, we achieve the SAP test for low-order errors except power with accuracy of 0.1 μm root-mean-square.
A new method combined subaperture stitching with interferometry(SSI) is introduced. It can test large and off-axis
aspheric surfaces without the aid of other null optics. In this paper the basic principle and theory of the technique are
analyzed. The synthetical optimization stitching model and effective stitching algorithm are established based on
homogeneous coordinates transformation and simultaneous least-squares method. The software of SSI is devised and the
prototype for testing of large aspheres by SSI is designed and developed. An off-axis asphere with the aperture of
376mm×188mm is tested by this method. For comparison and validation, the asphere is also tested by null
compensation.The synthesized surface profile is consistent to that ofthe entire surface from null test; and the difference
of PV and RMS error between them is 0.047 λ and 0.006 λ, respectively. So it provides another quantitative
measurement for testing large aspheric surfaces and off-axis aspheres besides null-compensation.
Studying the distribution of He+ in Earth's plasmasphere by detecting its resonantly-scattered emission at 304Å will
record the structure and dynamics of the cold plasma in Earth's plasmasphere on a global scale. EUV imaging systems
usually utilizes near normal incidence optics including multilayer mirror and filter. In this paper, the space condition of
the Earth's plasmasphere to confirm the expected performance of mirror and filter for this task were analyzed and some
guidelines for the design of the optical elements were introduced. In order to achieve higher response at 304Å and reduce
584Å radiation for the optical system, a new multilayer coating of Mo/Si with UOX (x=2~3) was developed, and it is
indicated that promising filter material is Al/C with a nickel mesh. In addition, we compute the reflectance of multilayer
mirror based on optical constants and the transmission of the filter based on atomic scattering factor. The results show the
multilayer mirror has high reflectance of 26.27% at 304 Å and low reflectance of 0.60% at 584Å. Finally, the conversion
efficiency of mirror coupled with filter is 6.88% at 304Å and 0.01% at 584Å.
Annular subaperture stitching interferometric technology can test large-aperture, high numerical aperture aspheric surfaces with high resolution, low cost and high efficiency without auxiliary null optics. In this paper, the basic principle and theory of the stitching method are introduced, the reasonable mathematical model and effective splicing algorithm are established based on simultaneous least-squares method and Zernike polynomial fitting. The translation errors are eliminated from each subaperture through the synthetical optimization stitching mode, it keeps the error from transmitting and accumulating. The numerical simulations have been carried on by this method. As results, the surface map of the full aperture after stitching is consistent to the input surface map, the difference of PV error and RMS error between them is -0.0074 λ and -0.00052 λ (λ is 632.8nm), respectively; the relative error of PV and RMS is -0.53% and -0.31%; and the PV and RMS of residual error of the full aperture phase distribution is 0.027 λ and 0.0023 λ, respectively. The results conclude that this splicing model and algorithm are accurate and feasible. So it provides another quantitive measurement for test aspheric surfaces especially for large aperture aspheres besides null-compensation.