基于菲涅耳衍射的无透镜相干衍射成像

Lensless coherent diffractive imaging with a Fresnel diffraction pattern

相干衍射成像是一种新型的无透镜成像技术,在光学测量、显微成像和自适应光学等领域有重要应用.本文提出一种基于单幅菲涅耳衍射强度图样的无透镜相干衍射成像方法;该方法采用特殊设计的卷积可解阵列抽样屏,通过对抽样物波的菲涅耳衍射强度图样进行非迭代的逆菲涅耳变换和滤波等数字处理实现被测物波复振幅信息的恢复,最后通过数字衍射得到物体的数字再现像.文中对抽样孔径、衍射距离、图像传感器尺寸等参数对再现像的影响进行了理论分析和模拟实验研究.发现在针孔大小和记录孔径大小一定的条件下,存在一个最佳的衍射距离;衍射距离过大会给重建图样带来噪声,衍射距离过小则会使再现象的分辨率降低.文中还对抽样针孔大小对系统成像分辨率的影响进行了分析,为进一步开展相关实验研究和应用提供了理论依据.

Coherent diffractive imaging is a new lensless imaging technique which has important applications in optical measurements, microscopic imaging and adaptive optics. We propose a method for coherent diffractive imaging from one single Fresnel diffraction intensity pattern. In this method, a Fresnel diffraction intensity pattern of the object wave passing through a specially designed sampling array is recorded and the complex amplitude of the object wave can be extracted through some digital processing such as inverse Fresnel transform and spatial filtering to the recorded intensity pattern; and then the image of the object can be reconstructed in computer. Some theoretical analyses and digital simulations about how the diffraction parameters affect the rebuilding image are given, such as sampling aperture, diffraction distance, image sensor size, etc. We find that there exists an optimal recording distance when the pinhole size and the recording aperture are given. Some serious noise will appear if the recording distance is longer than the optimal value, while shorter recording distance will result in a worse resolution of the reconstructed image. The influence of the pinhole size on the imaging resolution power of the system is also discussed. As this method requires only a single measurement of the diffraction intensity pattern and it does not need any iterative algorithm and lens systems, it provides a practically valuable approach to real-time wavefront measuring and lensless diffractive imaging of a complex-valued object in a wide rang of wavelengths.