基于微球体超级透镜的亚波长分辨率数字全息方法研究

The basic idea of all the super-resolution digital holography is mostly to acquire more far-field high frequency informations presently, and the near-field evanescent wave is usually neglected, so the sub-wavelength resolution can not be achieved. In this project, the digital holographic technology is combined with super-resolution imaging based on the microsphere superlens, and the sub-wavelength transverse resolution and the nano-level vertical resolution can be obtained in the digital holographic system. Aiming to the absence of the near-field propagation theory for the microsphere superlens, the effective diffraction model of the near-field wave, especially the evanescent wave will be established by three-dimensional vector diffraction theory, and the quantitative function to the near-field wave should be acquired with the parameters of the microsphere superlens. Numerical reconstruction algorithm with high resolution is developed using the mid-plane in the diffraction propagation process and the direct integral fast method, which is not restricted by the recording distance and CCD parameters. Based on the existing pre-magnification digital holography system, the sub-wavelength imaging function can be achieved with the microsphere superlens. The polarization multiplexing method is utilized to reduce the speckle noises. More near-field evanescent wave is collected by the multi-angle lighting mode to break through the diffraction limitation, and then the sub-wavelength resolution quantitative phase imaging can be reached. The research achievements can be applied to many fields such as the nanotechnology and life sciences, and possess great academic significance and application value.

当前超分辨率数字全息成像的出发点大多是如何获取更多的远场高频分量，而没有考虑蕴含亚波长信息的近场倏逝波，因此无法突破衍射极限分辨率。本项目将数字全息方法与基于微球体超级透镜的超衍射极限成像相结合，从而使数字全息成像具有亚波长的横向分辨率和纳米级的轴向分辨率。针对微球体超级透镜近场光波传播理论的缺乏，本项目基于三维矢量衍射理论，将建立有效的近场光波，特别是近场倏逝波的衍射传播和成像模型，定量确定微球体性能参数对光波复振幅的影响；利用衍射传播过程的中间平面和直接积分快速计算方法，发展不受再现距离和CCD参数制约的高分辨率数值再现算法；基于现有的预放大数字全息系统，实现基于微球体超级透镜的亚波长分辨率成像功能，采用偏振复用方法降低散斑噪声，利用多角度照明模式采集更多的近场倏逝波，突破衍射极限，实现亚波长分辨率定量相衬成像。项目成果可应用于纳米技术和生命科学等领域，具有重要的学术意义和应用价值。

本项目将数字全息与微球体透镜的超分辨率成像相结合，实现了微球超分辨率数字全息成像。理论分析了微球体成像的极限分辨率，给出了近场倏逝波可以传输到远场的临界条件，通过理论和仿真分析了微球体的折射率和半径对焦距、球差和数值孔径的影响，为优化微球成像提供了理论指导。结合像面数字全息成像与微球显微成像搭建了微球超分辨率数字全息成像系统，分别对一维和二维光栅进行了成像，获得了超分辨率的振幅和相位像。提出了基于振幅型空间光调制器的动态光栅超分辨率数字全息成像方法，理论推导了成像系统的点扩散函数, 定量确定了多个衍射级次再现像的分离条件，基于分辨率板实验验证了超分辨率性能。针对数字全息散斑的抑制，提出了基于角度多样化的快速自动散斑噪声抑制数字全息成像方法，利用纯相位空间光调制器加载不同的相位掩模板，精确和自动控制物体照明光波方向，使大幅度降低再现像的散斑对比度成为可能，大大提高了成像系统的稳定性和可操作性；提出了基于多角度无透镜傅里叶变换的数字全息的散斑噪声抑制成像方法，给出了矩形散射光斑的强度协方差，定量计算了退相关散斑图样的最小角度差，利用光纤端面在透镜焦平面的二维机械移动代替传统反射镜的旋转，大大提高了图像信噪比。