Fourier ptychography microscopy (FPM) shares its roots with the synthetic aperture technique and phase retrieval method, and is a recently developed computational microscopic super-resolution technique. By turning on the light-emitting diode (LED) elements sequentially and acquiring the corresponding images that contain different spatial frequencies, FPM can achieve a wide field-of-view (FOV), high-spatial-resolution imaging and phase recovery simultaneously. Conventional FPM assumes that the sample is sufficiently thin and strictly in focus. Nevertheless, even for a relatively thin sample, the non-planar distribution characteristics and the non-ideal position/posture of the sample will cause all or part of FOV to be defocused. In this paper, we proposed a fast digital refocusing and depth-of-field (DOF) extended FPM strategy by taking the advantages of image lateral shift caused by sample defocusing and varied-angle illuminations. The lateral shift amount is proportional to the defocus distance and the tangent of the illumination angle. Instead of searching the optimal defocus distance with the optimization search strategy, which is time consuming, the defocus distance of each subregion of the sample can be precisely and quickly obtained by calculating the relative lateral shift amounts corresponding to different oblique illuminations. And then, digital refocusing strategy rooting in the angular spectrum (AS) method is integrated into FPM framework to achieve the high-resolution and phase information reconstruction for each part of the sample, which means the DOF of the FPM can be effectively extended. The feasibility of the proposed method in fast digital refocusing and DOF extending is verified in the actual experiments with the USAF chart and biological samples.

中文翻译：

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快速数字重新聚焦和景深扩展傅立叶 ptychography 显微镜

傅立叶 ptychography 显微镜 (FPM) 与合成孔径技术和相位检索方法共享其根源，并且是最近开发的计算显微超分辨率技术。通过依次打开发光二极管 (LED) 元件并获取包含不同空间频率的相应图像，FPM 可以同时实现宽视场 (FOV)、高空间分辨率成像和相位恢复。传统的 FPM 假设样本足够薄并且严格对焦。然而，即使对于相对较薄的样本，样本的非平面分布特性和非理想位置/姿势也会导致全部或部分 FOV 散焦。在本文中，我们利用样本散焦和多角度照明引起的图像横向偏移的优势，提出了一种快速数字重新聚焦和景深（DOF）扩展 FPM 策略。横向偏移量与散焦距离和照明角的切线成正比。通过计算不同倾斜照明对应的相对横向偏移量，可以准确快速地获得样本每个子区域的离焦距离，而不是采用耗时的优化搜索策略来搜索最佳离焦距离。然后，将基于角谱（AS）方法的数字重聚焦策略集成到 FPM 框架中，实现对样本各部分的高分辨率和相位信息重建，这意味着可以有效地扩展 FPM 的自由度。在美国空军图表和生物样本的实际实验中验证了所提出的方法在快速数字重新聚焦和自由度扩展方面的可行性。