Diffractive optical characteristics of nanometric surface topography generated by diamond turning

High-precision optical components with nanometric surface finish can be obtained directly through single point diamond turning. However, residual cutting marks on the machined surfaces are likely to cause serious diffraction and deteriorate the optical performance of a machined component. This paper proposes a novel method for diffractive optical characterization of diamond-turned surfaces based on the vector diffraction theory. The distribution characteristics of the diffraction spots are revealed by using the finite-difference time-domain method. Simulation results supported by experimental verification demonstrate that the height and spacing of nanometric surface topography exert different influences on the intensity and angle of the diffraction spots. The intensity of high-order diffraction spots would be more prominent if a laser beam with a smaller wavelength and incident angle is used to illuminate the machined surface. Even if the areal surface roughness S_a changes less than 2 nm, the gray values of high-order diffraction spots may increase by nearly 5 times under certain conditions.