Polishing of large-aperture mirror and analysis of power spectral density

As the development of modern optical technology, especially space optical science, more high precision mirrors with large apertures are needed. But it is difficult to manufacture high precision large aperture optical components of multi-scale processing. The method of optical polishing using an ultra-precise bonnet was based upon the technology of computer controlled optical surfacing. A bonnet filled with air was applied as a precise polishing tool which was flexible and able to adapt itself well to the shape of the part, which was superior than other polishing methods. A material removing model of bonnet processed polishing was established according to kinematic principle based on the Preston equation. The model was modified in terms of Hertz contact theory using the physical characteristics of polishing bonnet tools. A satisfactory result was obtained for one of the surfaces of a wedge mirror with a diameter of 570 mm. The result of P-V and RMS parameters are 1/8λ and 1/75λ respectively. The PSD curves of the part and the noise of the narrow band are analyzed, as well as the reasons.