Abstract
Since the waviness on the surface of optical elements has a long period behavior, it is difficult to remove it accurately and rapidly by polishing. Therefore, in-process measurement technology that provides real-time feedback on waviness measurement results to the processing machine is required. Laser inverse scattering is a measurement technique that is suitable for in-process measurement and can perform three-dimensional measurements. The intensity distribution of the diffraction pattern generated by scattered light on the sample surface in the laser inverse scattering depends on the spatial frequency of the surface topography. Therefore, the phase distribution reflecting only waviness can be obtained by filtering out the intensity distribution other than the spatial frequency component of waviness. After the phase restoration, the waviness of the object can be obtained. To develop an in-process waviness measurement method, we propose a method to measure only waviness by filtering diffraction patterns using an optical spatial-frequency filter in the laser inverse scattering. In this report, simulations were performed to measure only waviness from shapes with waviness and roughness. Since the proposed method is different from conventional filtering methods, the amplitude transfer characteristics of the proposed method were investigated and compared with those of conventional filtering methods.
