基于螺旋相位调制的非相干全息点扩散函数研究

分析了菲涅耳非相干相关全息(Fresnel incoherent correlation holography,FINCH)系统中纯相位空间光调制器(spatial light modulator,SLM)加载螺旋相位掩模时的点扩散函数.以氙灯为照明光源搭建了FINCH系统,电荷耦合器记录的点源全息图与点扩散函数模拟结果一致.采用该系统分别在SLM上加载双透镜掩模和螺旋相位调制双透镜掩模两种情况下对分辨率板和非染色洋葱细胞成像,给出了成像对比结果.结果表明:采用螺旋相位调制的FINCH系统可以在几乎不牺牲分辨率的情况下提高图像的边缘对比度;同样,对相位物体也可以实现图像的边缘提取和识别.该方法在实时监测活细胞的分裂、形变等方面具有重要应用前景.

Point spread function of incoherent digital holography based on spiral phase modulation

Fresnel incoherent correlation holography (FINCH) has attracted much attention because it is able to record the holograms of three-dimensional (3D) samples under incoherent illumination with just a charge coupled device (CCD) and spatial light modulator (SLM). The FINCH technology achieves the splitting and phase shifting of the incident beam by loading a phase mask on an SLM. Three holograms, whose phase factors are different from each other, are recorded sequentially by a CCD. After the three holograms are superposed in the computer, the zero order image and a twin image are eliminated, and a complex hologram is obtained. The 3D properties of the object are revealed when the complex hologram is reconstructed in the computer. Spiral phase filters (SPFs) are commonly used to produce optical vortices, which can enhance and recognize image edges. In this paper, the spiral phase modulated FINCH system illuminated by Xenon lamp is built, in which the phase-only SLM is space-division multiplexed by a helical lens (superposed by an SPF and a lens) and a conventional lens. The mathematical model of spiral phase modulated FINCH system is established based on wave optics theory. The specific forms of the point spread function (PSF) and the reconstruction distance of the system are given for the first time. Experiments are conducted by using a small aperture with a diameter of 20 nm as a point source, the point source hologram recorded by CCD and the reconstructed image are consistent with the simulated ones. When the system is used for imaging resolution target and unstained onion cells, the edge contrast enhancement effects are obtained without the loss of resolution. The results show that the spiral phase modulated FINCH system can not only improve the edge contrast of the amplitude object, but also extract the edge information or recognition of the phase objects. This method has an important application prospect in the quantitative imaging of phase objects such as in real-time monitoring cell division and deformation of living cells.