An electromagnetic simulation model of microscopic scattering dark-field imaging was built based on the finite difference time domain (FDTD) method. The scattered light distribution of different defect’s size was obtained. Results show the span of distribution curve and the distribution peak are relative to the defect’s width and depth respectively. In the width range of 0.5 μm to 1 μm, there is a linear relationship between the distribution span and the defect’s width. Its goodness of linear fit reaches 0.9. Within the depth range of 0.1μm, the distribution peak linearly changes with the depth. But with the depth becomes deeper, the linear relationship between distribution peak and defect’s depth disappears. The results in this paper can provide instructive reference for the defect’s size inversion.
Point diffraction interferometer (PDI) has become the most promising measurement tool since it is firstly proposed by Linnik and its key component used to generate the reference wave can be called as the reference wave source (RWS). A new RWS based on the silicon nitride (SiN) waveguide is now proposed, aimed at providing a spherical reference wave with high NA and high accuracy. Simulation results show that the PV and the RMS of the reference wave generated by the waveguide RWS are 2.86×10-4λ (λ=532nm) and 4.83×10-5λ respectively, and the maximum light transmittance of this RWS could reach 24%. In addition, the NA of the reference wave reaches up to 0.58.
A method to simulate and design the dark-field imaging scene for optical spherical surface imperfection is proposed based on raytracing. Rays emit from the finite aperture camera model to the world space, split at the optical surface and finally obtain luminance from light sources. Thus the image function can be solved by raytracing and Monte Carlo integration of luminous flux. A typical dark-field imaging scene is presented, of which realistic images of various kinds of lens are rendered. The simulated images can well predict where the spots of light source locate and reveal imperfections. At last, corresponding adjustments are implemented to eliminate the influence of second surface.
To accomplish the interference testing to an off-axis parabolic mirror, we provided a kind of hybrid compensation modal combining compensator with stitching testing. To verify the validity of the above modal, we measured a Φ1450mm off-axis parabolic mirror with the above method. It can be seen from the stitching map that the stitching map is smooth and continuous in the full aperture. At the same time, to evaluate the stitching testing accuracy, we compared the stitching testing map and the subaperture testing map. It shows that the RMS of the residual map between them is 0.003λ, verifying the validity and accuracy of the model.
Subaperture stitching method is used for optics surface defects detection by defects imaging. Stitching based on position is efficient while stitching error induced by the error of the scanning mechanism may cause defects dislocation. According to the stitching error analysis of spherical optics defects, a method based on Monte Carlo simulation is proposed in this paper. Firs t the volumetric error model is established based on mult ibody system theory. On this basis, the stitching error model is established and applied to compute error by Monte Carlo simulation. Analyze error and then define the tolerance of the scanning mechanism to limit stitching error. Simulation results of an optical element whose diameter is 60mm show that the scanning mechanism should satisfy that the positioning accuracy and straightness in Y direction of X axis, the run-out errors in X and Y direction of B axis, and the verticality between X and Y axis are less than 1μm, the run-out errors in X and Y direction of C axis are less than 2.8μ m, the run-out errors of B and C are less than 4.6μm. Under such conditions, the stitching error will be less than 10μm.