The Fabrication Of Wolter-I Type Mirrors And The Measurement Of Surface Roughness

The grazing imaging system in the complex space soft X-ray and EUV telescope is mainly applied to the spatial environment monitoring and scientific studies for the solar and other celestial activities. Wolter-I structure is adopted in this system. So the fabrication and roughness measurement of the Wolter-I type mirrors are becoming the undergoing task for us.1) According to the special structure of Wolter-I type mirrors, a grinding&polishing system have been development for fabrication Wolter-I type mirrors, which has the functions of milling, grinding&polishing and in-situ inspection.2) Derive the removal function of small elastic sphere tool impacting on Wolter-I type mirrors with deflected rotating mode on the basis of Preston equation and Hertz contact theory. One of the removal models is that tool rotates but workpiece keeps static; and other is both tool and workpiece rotate.3) Correct the surface form by tools dwelling on each zone. Dwell algorithm for fabrication Wolter-Ιtype mirrors and the impacts of dwell steps on surface figure are investigated and analyzed. We choose the two step method for controlling the surface quality. When the ratio of tool-workpiece rotating angle velocity is 1.41, the surface quality is in the best state. In order to reduce the middle-high frequency errors, we adopt a arc shaped tool to polishing workpiece in oscillation motion with immersion type.4) The principle of measurement of super-smooth surface by grazing X-ray scattering method is introduced. The scattering diagrams measured on different samples are treated by first-order vector perturbation theory. The results indicate that the calculated PSD all are in a good agreement with the results obtained from Atomic force microscope (AFM). We also analyze the effects of the slit width of detector and the divergence of incidence X-ray on roughness measurement.The final surface figure of the mirror is 1.39μm (PV), 0.34μm (RMS) and surface roughness is 2.38nm (RMS) and the error of circularity is less than 0.1μm (RMS). Finally, the feasibility of fabrication Wolter-Ιgrazing mirror with deflected rotating mode method and method for measurement surface roughness are demonstrated by our experiments, benefiting to the advance of future work.