Tripathi Ashish, McNulty Ian, Shpyrko Oleg G
Opt Express. 2014 Jan 27;22(2):1452-66. doi: 10.1364/OE.22.001452.
Ptychographic coherent x-ray diffractive imaging is a form of scanning microscopy that does not require optics to image a sample. A series of scanned coherent diffraction patterns recorded from multiple overlapping illuminated regions on the sample are inverted numerically to retrieve its image. The technique recovers the phase lost by detecting the diffraction patterns by using experimentally known constraints, in this case the measured diffraction intensities and the assumed scan positions on the sample. The spatial resolution of the recovered image of the sample is limited by the angular extent over which the diffraction patterns are recorded and how well these constraints are known. Here, we explore how reconstruction quality degrades with uncertainties in the scan positions. We show experimentally that large errors in the assumed scan positions on the sample can be numerically determined and corrected using conjugate gradient descent methods. We also explore in simulations the limits, based on the signal to noise of the diffraction patterns and amount of overlap between adjacent scan positions, of just how large these errors can be and still be rendered tractable by this method.
叠层相干X射线衍射成像技术是一种扫描显微镜技术，无需光学元件即可对样品成像。从样品上多个重叠照明区域记录的一系列扫描相干衍射图案，通过数值反演来获取其图像。该技术通过使用实验已知的约束条件（在这种情况下是测量的衍射强度和样品上假定的扫描位置）来恢复因检测衍射图案而丢失的相位。样品恢复图像的空间分辨率受记录衍射图案的角度范围以及这些约束条件的已知程度限制。在此，我们探讨重建质量如何随扫描位置的不确定性而下降。我们通过实验表明，样品上假定扫描位置的大误差可以通过共轭梯度下降法进行数值确定和校正。我们还在模拟中基于衍射图案的信噪比和相邻扫描位置之间的重叠量，探讨了这些误差可以有多大并且仍能通过该方法处理的极限。
