Phase defect detection of large-aperture optics with static multiplanar coherent diffraction imaging.

Phase defect detection with micrometer scale on large aperture optical elements is one of the challenges in precision optical systems. An efficient scheme is proposed to detect phase defects. First, the defects are positioned in a large aperture by dark-field imaging based on large aperture photon sieves to improve the detection efficiency with a relatively low cost. Second, static multiplanar coherent diffraction imaging is used to retrieve the phase of the positioned defects in a small field of view. Here, a spatial light modulator is used as a multifocal negative lens to eliminate the mechanical errors in multiplanar imaging. The use of a negative lens instead of a positive lens has the advantage of a larger imaging space for the system configuration. Compared to the traditional interferometry system, this diffraction detection system has a simpler optical path and doesn't require sparse distribution of the defects. Experiment results demonstrate the success of the proposed scheme with a detection resolution better than 50 µm. We believe this work provides an effective method to rapidly detect phase defects on large aperture optics with high accuracy and high resolution.