Experimental And Theoretical Investigation On Correlated Imaging With Pseudo-thermal Light

Coincidence imaging, also called ghost imaging or correlated imaging, is a novel nonlocal imaging scheme. In this scheme, two spatial correlated beams (called test and reference in thermal and pseudo-thermal light) from a seminal light are employed. The test beam interacts with an object and then it is collected by a bucket detector (with no spatial resolution) and the reference beam is directly detected by a spatial resolution detector such as CCD. Though the reference beam does not interact with the object, the image of the object can be restored from the correlation of the bucket detector and the spatial resolution detector. Ghost imaging has been extensively investigated in recent years, both theoretically and experimentally. By using the second-order or high-order coherence properties of light field and the correlation measurement, coincidence imaging was realized with quantum entangled light, pseudo-thermal light and even true thermal light. The article mainly includes:1. Firstly, we give the definition of the coincidence imaging. Then, we briefly review the history of coincidence imaging and introduce the scheme of the coincidence imaging with entangled photon pairs and thermal light. Finally we analyze the theory of the coherent property of thermal light and give the expression of the coincidence function.2. In part two, we perform the ghost imaging with pseudo-thermal source. A pseudo-thermal source is firstly prepared by using a laser beam to pass through a rotating ground glass plate, and the parameters of the pseudo-thermal source are obtained via Hanbury-Brown-Twiss (HBT) experiment. With the pseudo-thermal light, we get ghost interference pattern. The experimental results demonstrate the accordance of numerical prediction. And our conclusion shows that the quality of ghost interference is influenced by the diameter of the pinhole in the reference path, the little pinhole due to a higher quality of ghost interference.3. With the theory of statistical optics, we construct the model of thermal light, and demonstrate the novel algorithm for image reconstruction. To deal with the data attained in the correlated imaging, we reorder the intensity recorded by the bucket detector according to the value of fluctuation. For a given fluctuation range with all the records over or below a specific value, we can obtain either positive or negative images by calculate the correlation between the selected records of the bucket detector and the reference detector. Nevertheless, without correlated calculations, positive or negative images can be also produced by directly averaging the corresponding records of the reference detector with positive or negative fluctuations. Meanwhile, the visibility of imaging is greatly enhanced. This correspondence imaging method further demonstrates the importance of intensity fluctuations in the nonlocal imaging with thermal light. We also experimentally show the images that obtained by the correlation method and the positive-negative correspondence imaging method, respectively. The results indicate that this novel algorithm has a better visibility than that of the correlated imaging.4. Based on the extended Huygens-Fresnel integral and the classical optical coherence theory, we derive the expressions for the visibility and signal-to-noise ratio (SNR) of lensless ghost imaging through turbulence. To show the effect of turbulence on the quality of lensless ghost imaging, we numerically calculate the visibility and SNR for different propagation distances and various turbulence strengths. Though turbulence degrades the image quality, specific visibility and SNR can be obtained for ghost imaging in certain propagation distances.5. We summary the mainly achievement and analyze application prospects of the coincidence imaging.