Lensless coherent diffractive imaging with a Fresnel diffraction pattern

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.