Autofocus Method of Lunar Surface in-Situ Scanning Electron Microscope Based on Gaussian Defocus Model

Lunar resources and environment exploration payload is the focus of space projects of various space powers. The miniaturized Scanning Electron Microscope (SEM), which is widely used to analyze the morphology, composition and structure information of microscopic materials and substances, is a suitable payload for the exploration of lunar soil and rock structure and composition. Compared with the large bench scanning electron microscope in the laboratory, the micro electron microscope used for the in- situ exploration of the lunar surface puts forward higher requirements for the power consumption, efficiency and response speed of the control algorithm. The adaptive autofocus algorithm of electron beam is the core algorithm to drive the load. In this paper, an autofocus method based on Gaussian defocus model is proposed. The images collected by Zeiss scanning electron microscope and MATLAB simulation show that compared with the traditional method based on search algorithm, the proposed method significantly reduces the number of sampling frames and improves the focus speed.