Study On High Spatial Resolution Coherent Diffraction Imaging Method Based On Single X-ray Exposure

Coherent Diffraction Imaging(CDI)is a lensless Imaging method that uses a two-dimensional detector and a computer to take the place of the lens,and its theoretical imaging resolution is limited by the wavelength of the incident light.After years of development,this method has been widely used in synchrotron radiation light source,X-ray free electron laser light source(XFEL)and other large-scale scientific facilities to obtain two-dimensional or three-dimensional images of samples in materials,biology,environment and other research fields.According to the number of diffraction patterns used to reconstruct images,coherent diffraction imaging methods can be divided into scanning CDI(Ptychography)and conventional single exposure CDI.Ptychography is widely used in synchrotron radiation light source because of its advantages such as fast convergence,nice imaging quality and no limit of samples.However,the multiple exposures required by the Ptychography method make it unsuitable for some special occasions like free electron laser.By contrast,although the conventional CDI method has disadvantages such as slow convergence,poor imaging quality,and the isolated sample requirement,it does not need multiple exposure of samples,so its application range is wider than Ptychography method.At present,CDI method still occupies an important position in X-ray imaging.Based on the international cutting-edge research trend,this paper mainly focuses on the improvement of single exposure CDI method with two directions: 1.Drawing on the overlapping areas and other concepts of Ptychography method and applying them to CDI method to improve the reliability of CDI method.2.Improving existing three-dimensional imaging method and developing three-dimensional imaging technologies suitable for CDI methods.The main achievements are as follows:1.Spatial correlated coherent diffraction imaging method is proposed.The idea of this method comes from the concept of overlapping areas in scanning CDI and the application of markers near samples in X-ray holography.Spatial correlated coherent diffraction imaging method artificially creates the correlation by adding the same artefact around each isolated sample to improve the image reconstruction quality of CDI method and the robustness of the whole reconstruction process.In theory,thismethod can be used in free electron laser devices or other special cases where scanning CDI is difficult or not suitable for application.We verify the effect of this method through visible light experiment,and explore the influence of some experimental parameters in this method on the imaging effect through simulation experiment.2.The method of reconstruction of incident light information(probe)is improved.The reconstruction of incident light information in the algorithm is conducive to improve the imaging quality of the reconstructed image,while the concept of the reconstruction of incident light information in the CDI method(proposed by Takahashi et al.in 2016)comes from the algorithm of the reconstruction of incident light information in Ptychography.In the work of this paper,we found that the incident light information reconstruction in CDI method must satisfy the "dislocation" condition,which is verified by numerical simulation and optical experiment.The condition of "dislocation" must be satisfied to reconstruct sample and the probe images successfully.At the same time,we also verify the improvement of imaging quality of probe reconstruction CDI compared with traditional CDI through visible light experiment.3.The method of double-beam Ankylography is introduced.The double-beam Ankylography method is proposed to solve the problem of low resolution of the third dimension(along the direction of light path)of the Ankylography method.In the double-beam Ankylography method,it is necessary to divide one beam into two beams and then converge them to a point to exposure the sample,which has certain requirements for the experimental device.The previous work provides a reference for the design of the device.In this paper,a visible light experiment is carried out to verify the improvement of the resolution of double-beam Ankylography compared with the conventional Ankylography in the third dimension,then it is found that the angle of two beams will affect the reconstruction quality of the 3d image of sample.Through numerical simulation experiments,we also explored the most suitable angle for the double-beam Ankylography method.