The Research Of Differential Phase Contrast Imaging System Based On Four Quadrant Liquid Crystal Device

With the continuous exploration of the field of life sciences,the observation of microscopic tissues such as cells has become increasingly important.However,most biological tissues and cells are colorless and transparent,with a low optical absorption coefficient.In the case of undyed condition,it is difficult to observe cells detailed information under traditional bright field microscopy.In order to solve this problem,non-invasive,unmarked quantitative phase imaging technology has emerged.Differential phase contrast imaging(DPC)is a good quantitative phase observation method,which can solve phase information invisible to the human eye from the light intensity information obtained by the camera,and has robustness.In order to improve the imaging quality and implement practical application of differential phase contrast imaging,the following research work has been carried out in this paper:1.Starting with the principle of phase contrast imaging,the development process of differential phase contrast imaging is reviewed,and the quantitative differential phase contrast imaging model is derived.A L2 regularization method using a mixed constraint of constant coefficients and gradient operators is proposed to solve the problem.For random noise with a variance of 0.04,compared to the traditional L2 regularization method,the mean square error of the reconstructed image is reduced from 0.0135 to 0.0047.2.In order to realize the lighting function modulation requirements of differential phase contrast imaging technology,an illumination module based on four quadrant liquid crystal devices was proposed,and an embedded four quadrant twisted liquid crystal device was designed and fabricated.Theoretical analysis has shown that the factors that affect the performance of liquid crystal devices include device thickness,illumination center wavelength,and liquid crystal material parameters.Under the condition of a central wavelength of 550nm,the device thickness was determined to be 4 μm.Use liquid crystal material on of 0.12.A twisted liquid crystal device with high transmittance and low response time was prepared and experimentally verified,with a thickness error of less than 0.5%.The performance of liquid crystal devices was tested,and the transmittance of the bright state reached 40%,the contrast reached more than 1200:1,and the response time was 19.6ms.3.A differential phase contrast imaging system based on four quadrant liquid crystal devices is designed.The liquid crystal devices are coupled to the front focal plane of the systems condenser to achieve asymmetric illumination control functions for differential phase contrast imaging.The prepared miniaturized liquid crystal device can be directly coupled with existing commercial microscopes,mainly including:(1)coupling with an upright transmission microscope OLYMPUS-CX23,wherein the size of the liquid crystal device is 22mm × 18mm.The quantitative phase imaging function of the system was verified through quantitative phase imaging experiments with a micro-convex lens array,with a reconstruction accuracy of 98%and a Pearson correlation coefficient of 0.9947.(2)Coupled to an inverted transmission microscope OLYMPUS-CKX53,the four-quadrant liquid crystal device has a size of 54mm × 50mm.Quantitative phase imaging of living embryonic stem cells has been achieved.Experimental results show that using L2 regularization with constant coefficients and gradient operators,the results of quantitative phase reconstruction have good imaging contrast,suppress noise,and obtain higher quality phase images.This thesis focuses on liquid crystal differential phase contrast imaging systems,designing and fabricating liquid crystal devices with good performance as the lighting control method of the system.The mixed constrained L2 regularization method reduces the impact of noise on phase reconstruction,which has important driving and guiding significance for the practical application of liquid crystal differential phase contrast imaging systems.