Accurate reconstruction for the measurement of tilt surfaces with digital holography

Digital holography has been widely applied in the measurement of complex micro–nano structures. The reconstruction of the object wavefront is usually under the assumption that the measured sample is parallel to the recording plane, which means the diffraction distance is fixed. While the tilt of the measured sample is inevitable, especially for the scanning measurement of a large component where the movement will introduce inclination. Then ringing artifacts will occur, which seriously affect the quality of the reconstructed wavefronts. In this paper, an accurate diffractive reconstruction method is proposed. A pose transformation model is established for calculating the accurate diffraction distances of the tilt wavefronts. The gradient of the reconstructed complex amplitude is utilized in the merit function for the pose estimation. By minimizing the merit function, the pose parameters can be refined with the particle swarm optimization. Experimental results demonstrate that the proposed method can effectively improve the reconstruction accuracy of the tilt wavefronts. It is significant for the scanning measurement of large components.