The Research Of The Influence From The Positive And Negative Defocusing On Classical Thermal Light Lensless Ghost Imaging System

Correlated imaging,is called ghost imaging,also know as quantum imaging or two-photon correlated imaging,which is the forefront of cross-disciplines of quantum mechanics and optical imaging in recent years.It is a nonlocal imaging technique which can obtain the image or Fourier transform image of an imaging object by correlating the intensity fluctuations of the two optical paths.Compared to traditional imaging,correlated imaging has more advantages because of its nonlocal characteristics.Correlated imaging technology has a broad application prospects,which can be used for laser radar,satellite communications,infrared imaging,medical imaging and military aspects,etc.At present,some research scholars have combined some advanced image processing algorithms into the ghost imaging technology to obtaining the high-quality ghost-image.In this paper,the influence of positive and negative defocusing on lensless ghost imaging and ghost diffraction system is studied deeply,and the influence of the detector size on lensless ghost imaging system is also analyzed.The specific research content and innovation of the paper are as follows:Firstly,when we discussing the effect of the positive and negative defocusing on the lensless ghost imaging,the positive defocusing is obtained by reducing the length of the test arm and the length of the reference arm is constant,while the negative defocusing is obtained by reducing the length of the reference arm and fixing test arm length.Based on the Huygens Fresnel diffraction integral formula,the mathematical expression of the point spread function in the lensless ghost imaging system is derived.The expression can be used to describe the imaging resolution,i.e.,the smaller the width of the point spread function is,the higher the resolution of the image is,and vice versa.We also use the fidelity to analyze the impact of positive and negative defocusing on the ghost imaging system.It is verified with the results of the experiment and numerical simulation.Concluding that the system has the best image quality when there is no defocusing,and both positive and negative defocusing will reduce the image quality.When the two defocusing lengths are equal,the effect of positive defocusing is smaller.In addition,the same conclusions can be obtained in the far field.Secondly,the test detector in the ghost imaging system is a bucket detector,using the integral of the detector to discuss the influence of its size on the ghost imaging system.The results of the numerical simulation and experiment show that the image quality increases with the increase of the test detector size.When the size of the detector increases to a certain extent,the image quality is basically remain unchanged.Therefore,we should choose the appropriate size of the detector when designing the ghost imaging system experiment.Finally,the influence of the positive and negative defocusing on the lensless ghost diffraction system is also studied.Through the theoretical analysis and numerical simulation,it is found that the results are similar to that in the ghost imaging system,namely,when the positive defocusing and negative defocusing lengths are equal,the negative defocusing has a greater effect on the ghost diffraction system,and the imaging quality is the best when there is no defocusing.