Research On Phase Retrieval On Weakly Scattering Sample With In Coherent Illumination Source

With the development of science and technology, the demand of disease detection is increasing sharply. High precision detection tools are also needed and the detection accuracy is microns or even nano-scale. As a high precision detection tool, optical detection tools are widely used in biological detection. Biomedical Photonics is a research direction which highly integrating the optics and medicine.Due to its high frequency, it's very hard for charge-coupled device(CCD) or other recorders to record phase information of a sample. As the scenery we can see in the microscopy, the information we can only detect is amplitude. However, phase contains too much significant information such as the sample's configuration, depth, three dimensional structure and so on. As a result, it's very necessary to detect phase information. Base on whether the phase can be precisely detected, the phase detection technology can be divided into two categories: qualitative and quantitative phase detection methods. Phase contrast microscopy and differential interference phase contrast microscopy belong to the former. Holography, Hartmann wavefront sensor, transport of intensity equation(TIE) are geared to the later. However, these technology suffer from different problems such as complex devices, low resolution, aberration and so on. As a lensless technology, coherent diffraction imaging(CDI) avoid these shortages and is widely used in the area of medical detection.Ptychographic Iterative Engine(PIE) has aroused worldly attention due to its wide imaging field and high convergence speed. As same as CDI, PIE also requires completely coherent illumination source. However, it's very hard for sources like X-ray or electron beam to meet this requirement. While illuminated by these sources, the reconstructed pattern will be ambiguous. It is of significant importance to develop a new algorithm to handle the incoherence of the illumination. PolyPIE algorithm is introduced in this paper while bringing the spectral component of the light source into the iterative computation. The image of the object and the illuminating probe are reconstructed for each spectral component. This method can be widely used in the imaging field of X-ray or electron beam illumination. Combined with ePIE algorithm, E-PolyPIE algorithm is proposed which can reconstruct the sample and the distribution of the probe simultaneously.However, synchrotron radiation sources such as Shanghai synchrotron radiation source or Swiss synchrotron radiation source, they suffer from partially coherent problems. How to reconstruct clear images while illuminated by these sources is an urgent problem needed to be solved. In this paper, through analyzing the ingredients of the diffraction patterns, we find the bright field area also can be regarded as pure coherent diffraction patterns composed of a strengthened zeroth order beam and a weaken diffracted beam. The dark field area generated by interference of diffracted beams cannot meet the requirement of coherence. Moreover, in order to enhance the details of weakly scattering samples in reconstruction, high order iteration of bright field area is proposed in this paper. The contrast of weakly scattering sample is obviously improved and the details can be reconstructed clearly through this method. We verify this method with simulation and experiment, the sample information can both be reconstructed clearly.In this paper, we did some research on the incoherence of illumination source in the field of Ptychographic Iterative Engine. By adding the component of the source into iterative computation and using the bright field while reconstruction, the details of the sample can be reconstructed clearly. For weakly scattering samples, high order iterative method was introduced in this paper to enhance the contrast of reconstructed images. These method can wildly expand the application fields of the PIE.