Research On Wide-field High-resolution Quantitative Phase Microscopy Methods Based On Fourier Ptychography

"Wide-field high-resolution imaging" and "quantitative phase imaging" play crucial roles in diverse applications such as optical microscopy and biomedical science.Based on the traditional optical microscopy theory,in recent years,a new technology named computational optical microscopy provides novel schemes,theories,and methods for obtaining quantitative high-resolution phase images in large FOV.Among these computational microscopy techniques,the most representative one is Fourier ptychographic microscopy(FPM).A systematic research has been conducted in this doctoral dissertation to explore the key theories associated with FPM.It is expected to address several key issues in FPM,which improves the imaging quality,measurement accuracy,imaging through-put,SBP,imaging efficiency,and temporal resolution of FPM-based wide-field high-resolution quantitative phase microscopy techniques,enabling us to obtain dynamic quantitative phase information of label-free specimens with millimeter FOV,submicron spatial resolution and millisecond temporal resolution.The main research work and innovation points are summarized as the following aspects:(1)An optimal iterative reconstruction algorithm based on adaptive step-size has been proposed,which solve the FPM solution astringency problem under noisy conditions.The convergence of the optimal iterative solution for convex problems is proved mathematically.After classifying and summarizing the developed FPM optimization algorithms,the convergence characteristics of the global gradient method and the incremental gradient method are analyzed under noisy conditions.And finally an incremental gradient algorithm with adaptive step-size is proposed.By maintaining the high convergence speed and computational efficiency,the noise resistance of FPM are significantly improved under noisy conditions.(2)A positional misalignment correction method based on simulated annealing and non-linear regression has been introduced.The mathematical model of the most influential and critical factor,the LED positional misalignment,is carried out.And then,aiming to minimize the reconstruction cost function,the simulated annealing algorithm and the non-linear regression algorithm are utilized to obtain the global positional misalignment parameters for the entire LED array.Compared with the traditional simulated annealing method,our method significantly improves the efficiency and robustness of LED positional misalignment correction due to the local initial correction and the global nonlinear regression.(3)An optimal sampling criteria in object space and frequency space has been proposed for FPM.Dealing with the problem of low measurement efficiency occurred in traditional FPM technology,which usually needs a large amount of redundant information,the minimum requirement of sampling redundancy for FPM is analyzed.The optimal sampling criteria in object space and frequency space are proposed.Finally,according to the sampling criteria provided above,we present an illumination angle subsampled FPM method,which takes the least redundancy of the original images and recovers the most high frequency information,providing a guideline for designing an optimal FPM system.(4)A high-throughput experimental FPM system(REFPM)has been proposed based on a programmable LED condenser with large illumination NA.By utilizing a low magnification objective lens,a LED array based oil immersion condenser can be used to increase the illumination NA to 1.2.In order to ensure the reconstruction accuracy,a high-density LED array is mounted on the front focal plane of the condenser to satisfy the optimal sampling criteria.It is the first time that a FPM system realizes a synthetic numerical aperture of 1.6 using a lOx objective and a half-pitch resolution of 154nm,which achieves a large SBP nearly 50 times higher than that of the conventional incoherent microscope with the same resolution.(5)Two new experimental systems have been proposed for realizing dynamic quantitative phase microscopy based on FPM.It is the first time that a systematic and comprehensive analysis of the optical transfer function of FPM method is derived.When the maximum bright-field illumination angle equals the numerical aperture of the objective,the phase transfer function can cover all the low-frequency phase components.Based on this conclusion,a high-speed FPM technique based on annular illuminations is proposed.With only 4-12 bright-field images,high-quality phase distribution can be recovered with a maximum frame rate of 25 FPS.Further more,a single-shot FPM system based on color multiplexing is proposed,which simultaneously illuminates the object with three different wavelengths and the matched illumination angle.Finally,wide-field high-resolution phase distribution is recovered from the single-shot image,and the phase imaging frame rate reaches 50 FPS for the first time.