Research On Lensless Ptychography Via Multi-Angle LED Illumination

For a long time,in the field of optical microscopy imaging,there has always been a certain competitive relationship between a large field of view and high resolution.How to take an effective way to ensure that the imaging has a large field of view and high resolution at the same time.Ptychographic microscopy is an emerging lensless phase recovery technology in the past ten years.It not only has the advantages of large field of view and high resolution,but also greatly improves the convergence,speed,and anti-noise ability of traditional phase iterative recovery algorithms.It has had widely used in many fields.Today’s ptychographic microscopy imaging is based on a high-efficiency computer,which illuminates different parts of the sample through incident light waves at different angles,and requires each illumination to overlap with other parts.We can regard each illumination as "Layer",the overlapping of layers with each other are "Ptycho",and the result is obtained through iterations.Starting from the principle of ptychographic microscopy imaging,this thesis introduces the imaging system,method,and reconstruction algorithms of ptychographic microscopy.And conducts specific analysis and research on the key parameters of them,focusing on the investigation and analysis of phase recovery algorithms.The effectiveness of,and to explore and improve the reconstruction efficiency and image reconstruction quality:(1)A corresponding solution is proposed for the problem of poor anti-noise capability in the phase recovery algorithm.In traditional ptychographic microscopy imaging,the phase recovery algorithm based on a incremental gradient is widely used due to its superior computational efficiency and flexibility.However,since the sensor usually collects various noises,the reconstruction result will drop sharply.In this regard,the key issue is how to control and design the step calculation in the algorithm.Therefore,this thesis proposed a loss correction algorithm based on ptychographic microscopy imaging.In the algorithm,we added a loss correction term,and adjusted the step size according to the value of this term,which can effectively improve the convergence performance of the algorithm and significantly improve the anti-noise ability of the algorithm.Compared with the classical method,simulations and experiments have proved that our method is superior to the classical method in terms of efficiency and quality.At the same time,the calculation results show that the initial step size can be appropriately increased to increase the speed of convergence without reducing the reconstruction quality.At the same time,for the LED angle correction,we cross-correlate the measured diffraction pattern and its corresponding estimated value to improve the reconstruction quality.(2)Analyzed the refocus problem in ptychographic microscopy,and introduced the principle of refocusing algorithm in detail,mainly to accurately estimate the "z distance" in its imaging system,and through reconstruction to add more detailed information to the result image,and Experiments have verified the effectiveness of the refocusing algorithm.At the same time,the effective combination of the phase recovery algorithm and the refocusing algorithm in the ptychographic microscopy imaging first improves the quality of the low-resolution images collected,and then in the subsequent iterations,the result image with higher definition can be reconstructed.Through simulation and real shooting experiments,it is verified that the method can effectively solve the defocus problem and improve the clarity of the reconstruction results.