Analysis of diffraction wavefront in visible-light point-diffraction interferometer

As a key element in point-diffraction interferometer (PDI), the diffraction pinhole determines the sphericity of the reference wavefront and achievable precision of the testing system. The point-diffraction wavefront error, aperture angle, and light transmittance in the PDI operating at visible light, which are determined by pinhole dimension, are analyzed based on finite difference time domain (FDTD) method. The study shows that an aperture angle about 75° can be obtained with a 1 μm pinhole diameter, and the corresponding testing precision is better than root mean square λ/1000 within 0.35 NA. Both the numerical simulation and experiments have been carried out to demonstrate the feasibility of the proposed analysis approach, and a good agreement is obtained between calculated and measured parameters in visible-light PDI. The proposed simulation approach with the FDTD method provides a feasible way to analyze the diffraction wavefront in visible-light PDI, as well as a powerful tool for the design and optimization of PDI system.