May 13, 2020
Recently, Zhu Jianqiang, the research team of high power laser physics Joint Laboratory of Shanghai Institute of Optics and precision machinery, Chinese Academy of Sciences, has made new progress in the research of phase defect detection of large-diameter optical elements and proposed a new detection scheme combining dark-field imaging and static multi-plane coherent diffraction imaging. The relevant results were published in Applied Optics on May 7.
The UV damage of the terminal optical element is one of the bottlenecks restricting the development of high-power laser driver at present, and the damage of the downstream optical element caused by the enhancement of the optical field of the micron size phase defect is one of the main causes of the damage of the terminal optical element at present, so the precise detection and control of the phase defect of the large-diameter optical element improves the load capacity of the high-power laser device Ascension is essential. How to detect the local phase defects of large aperture (300 ~ 400mm) components with micron-scale efficiently and accurately is an international problem.
The research team proposed a "two-step" solution to solve the above problems. The first step is to use the dark field imaging technology based on the large aperture photon sieve to locate the phase defects in the full aperture range, greatly improving the detection efficiency and reducing the system cost; the second step is to use the static multi-plane coherent diffraction imaging technology (MCDI) to measure the phase defects accurately in the small field of view, and use the spatial light modulator as the focusing lens to avoid them It avoids the mechanical movement error of traditional MCDI and improves the system stability.
Compared with the traditional interferometric method, the optical path of the diffraction measurement system proposed in the "two-step" scheme is simple and has no special requirements for the sparsity of defect distribution. The experimental results show that the resolution of the system is better than 50 μ m, which meets the current detection requirements. This research provides a new effective solution for the high-efficiency and high-precision detection of phase defects in large-aperture optical elements.
Relevant research has been supported by the NSFC, Shanghai Natural Science Foundation, research instrument, and equipment development project of the Chinese Academy of Sciences and youth innovation promotion association of the Chinese Academy of Sciences.
Figure 1 phase defect detection system based on static multiplane coherent diffraction imaging
Figure 2 phase reconstruction results under different iterations (a ~ F) are 1, 2, 5, 10, 50, 200 respectively)