Surface measurement by CMM is the main method in the process of large-aperture high order aspheric mirrors fabrication. Because of the existence of probe-radius error in measurement data, the achieved surface residual cannot be directly used in mirror fabrication. So the Probe-Radius Compensation Based on Aspherical Surface Reconstruction is proposed. The algorithm comes up with a high precision surface fitting model, which introduces coordinate system space deviation parameters and use this model to calculate compensation vectors to correct the probe-radius error. The experiment shows that there is only a deviation of 4nm between the corrected data and the real data and fully meets the needs of optical fabrication.
The large-caliber light-weight reflector assembly is the core optical component of the large-size space camera. It needs to be highly light-weight to meet the constraint of emission weight. At the same time, the on-orbit reflector assembly needs to have extremely high force and thermal stability, be able to withstand the changes in the in-orbit temperature environment and the resulting stress changes and maintain the profile quality. This paper introduces the development of 1.3m caliber space mirror module. The reflector adopts the uniform thickness back arc design and the positioning support adopts the six-bar Bipod support technology. The simulation analysis verifies that the reflector component has good force and heat stability. The optical axis vertical test is carried out on the surface of the reflector assembly which has been processed and adjusted. The test results are consistent with the mechanical analysis results of the reflector assembly under the condition of gravity field, which meets the technical requirements of the spatial reflector.
Edge-trimming experiment of a reflective mirror is carried on in the paper to study the influence of edge-trimming on the surface figure of a reflective mirror. First, the influences of both self-gravity and the supporting method in measuring on the surface figure of the same mirror before and after edge-trimming are simulated. The simulation results show that both self-gravity and the supporting method in measuring have little influence on the surface figure. Second, the real surface figure of the mirror before edge-trimming is calibrated. Third, edge-trimming experiment of the mirror is carried on the ultrasonic grinding machine. Forth, the real surface figure of the mirror with the same effective aperture after edge-trimming is calibrated. The measuring results show that the surface figure of the mirror after edge-trimming is changed greatly in comparison of that of the mirror before edge-trimming: the surface figure of the mirror before edge-trimming is that the root-mean-square value (RMS value) is about λ/40 (λ=632.8nm), while the RMS value of the surface figure of the mirror after edge-trimming is about λ/15. At last, the mirror is polished again. The final RMS value of the surface figure of the mirror is about λ/40. The experimental results show that edge-trimming can bring stress to the mirror. Therefore, edge-trimming influences the surface figure of the mirror considerably. The consequent polishing experiment can erase the influence. The experiment shows that edge-trimming can be carried on with the reflective mirror with lower surface precision. The whole experiment will provide some helpful reference on the choice of edge-trimming occasion of the reflective mirror if it is necessary.
Base on the special characters of off-axis spherical and three-axis ion beam figuring (IBF) system, a method of obtaining the removal function depending on incidence angles are introduced and the curve be indicated. Keeping the fabrication coordinate coincident to the optical coordinate can avoid the transformation of interferometry map, which could introduce the distortion error. By analyzing of the process of polishing the 562mm×290mm off-axis mirror, the polishing experimentation has been carried out on the IBF2000 system developed by NTG. After two iterations and 37.2 hours polishing time, the RMS value of surface accuracy is from 0.033λ to 0.016λ, and the mid-spatial error mitigated dramatically. The experimentation indicates that using the non-contacting polishing feature of IBF with reasonable optimizing process, the surface accuracy and the mid-spatial error can be improved simultaneously.
The convex hyperbolic secondary mirror is a Φ520-mm Zerodur lightweight hyperbolic convex mirror. Typically conventional methods like CCOS, stressed-lap polishing are used to manufacture this secondary mirror. Nevertheless, the required surface accuracy cannot be achieved through the use of conventional polishing methods because of the unpredictable behavior of the polishing tools, which leads to an unstable removal rate. Ion beam figuring is an optical fabrication method that provides highly controlled error of previously polished surfaces using a directed, inert and neutralized ion beam to physically sputter material from the optic surface. Several iterations with different ion beam size are selected and optimized to fit different stages of surface figure error and spatial frequency components. Before ion beam figuring, surface figure error of the secondary mirror is 2.5λ p-v, 0.23λ rms, and is improved to 0.12λ p-v, 0.014λ rms in several process iterations. The demonstration clearly shows that ion beam figuring can not only be used to the final correction of aspheric, but also be suitable for polishing the coarse surface of large, complex mirror.
Based on Zerdour, quartzs, developing Experimental process by ultrasonic drilling and milling, analyse the results of the
Process Parameters of various . With a lightweight plane mirror as an example, The processing results show that the
lightening ratio of plane mirror is as high as 45%, the roughness is higher than 2 μm.
A zerodur mirror whose aperture is 900mm is chosen to be the primary mirror of an optical system. The mirror is polished by rapid polishing and precision polishing methods relatively. The final surface figures of the mirror are as follows: the peak-to-valley value (P-V value) is 0.204λ (λ=632.8nm), and the root-mean-square value (RMS value) is 0.016λ, which meet the requirement of the optical system. The results show that the polishing process is feasible.
The null compensator is the most commonly used method in the large aperture aspheric mirrors manufacturing and testing process. Combining the testing equipment which have already existed, spherical wave compensator and plane wave compensator are need to be designed separately in the practical application. Based on the third-order aberration theory, the equations of two-1ens compensators for 1.5m, F/1.33 hyperboloid concave mirror are deduced, and two different kind design methods for two-lens compensator are obtained. The optimized compensate system achieve the accuracy of 0.0025λ (PV) and 0.0007λ (RMS) by using the optical simulation analysis software. At last, the manufacturing tolerance and compensating range are analyzed, and the result of which indicates that the optimized result are rational and reliable, and it can fulfill the requirement of manufacturing and testing process for aspheric mirrors, meanwhile, the design can lay a theoretical foundation for the null test of larger F/# primary mirror.
The surface profile of Wolter type-I mirror has a great impact on the performance of Solar X-ray Telescope. According to the existing fabrication instrument and experimental conditions in our lab, an
in situ Long Trace Profiler is developed and set up on the fabrication instrument in order to measure the surface profile of Wolter mirror in real time during fabrication process. Its working mechanism, structural parameters and data processing algorithm are investigated. The prototype calibrated by a standard plane mirror is used to measure a sample of Wolter type-I mirror. The results show that our prototype can achieve an accuracy of 2.6μrad rms for slope error with a stability of 1.33μrad during the whole measurement period. This can meet further fabrication requirements.
A soft x-ray reflectometer with laser produced plasma source has been designed, which can work from wavelength 8nm
to 30 nm and has high performance. Using the soft x-ray reflectometer above, the scattering light distribution of silicon
and zerodur mirrors which have super-smooth surfaces could be measured at different incidence angle and different
wavelength. The measurement when the incidence angle is 2 degree and the wavelength is 11nm has been given in this
paper. A surface scattering theory of soft x-ray grazing incidence optics based on linear system theory and an inverse
scattering mathematical model is introduced. The vector scattering theory of soft x-ray scattering also is stated in detail.
The scattering data are analyzed by both the methods above respectively to give information about the surface profiles.
On the other hand, both the two samples are measured by WYKO surface profiler, and the surface roughness of the
silicon and zerodur mirror is 1.3 nm and 1.5nm respectively. The calculated results are in quantitative agreement with
those measured by WYKO surface profiler, which indicates that soft x-ray scattering is a very useful tool for the
evaluation of highly polished surfaces. But there still some difference among the results of different theory and WYKO,
and the possible reasons of such difference have been discussed in detail.
Application of the x-ray scattering (XRS) technique for studying super-smooth surfaces such as Si wafers is discussed.
The XRS method is demonstrated to enable quantitative evaluation of power spectrum density (PSD) functions and
effective roughness of super-smooth surfaces. Within the calculation of PSD functions, comparative study between
first-order vector perturbation theory (FOPT) and generalized Harvey-shack theory (H-S) is performed. First-order
perturbation theory which is widely accepted and has been extensively validated even for large scattered and incident
angles for "smooth" surfaces considers the scattering amplitude as a power series in the roughness height; its scattering
diagram is related to the statistical parameters of surface roughness (PSD functions) in a very simple way (linear).
Therefore, PSD functions can be uniquely and directly extracted from the measured data. However, generalized
Harvey-shack theory considers that scattering behavior is characterized by a surface transfer function which relates the
scattering behavior to the surface topography. With the grazing incident angle less than critical value about 0.22 degree,
three Si wafers with rms roughness of 0.29nm, 0.46nm and 0.67nm are inspected by XRS (λ=0.154nm) method. The
calculated values are all in a good agreement with the results obtained from Atomic force microscope (AFM). However,
the difference resulting from the limits of applicability of the theories used in XRS data processing appears and be
analyzed. Both of the theories are not only used for optical surface characterization, but also can allow accurate
predictions of image degradation due to scattering effects in grazing X-ray telescopes. The experimental schemes are