Research On The Influence Of The Internal And External Factors On The Quality Of Ghost Imaging

Ghost imaging is a novel non-local imaging technique,it is given wide attentions because of its high robustness to noise,and high lateral resolution.As a computational imaging technique based on intensity fluctuation correlations,compared with conventional optical imaging techniques,ghost imaging has two significant disadvantages: its poor imaging quality and imaging efficiency.ghost imaging technique will become more and more important in the field of both imaging and detecting when these issues are improved.In order to find the reason caused the affected imaging quality,this dissertation carried out a series of theoretical researches based on both internal and external factors which affect the imaging quality of ghost imaging technique,also,we gave the methods to solve these problems.In the aspect of internal factors,the second-order correlation function,which is the core of ghost imaging technique is investigated.A theoretical structure based on statistical weighted average expatiation of ghost imaging is established.Under this structure,the entire progress of image reconstruction is studied.As an important result,it is found that the positive and negative phenomenon is also existed in computational ghost imaging system.In this dissertation,a criterion to distinguish the positive and negative correlations is given,the positive and negative correlations can be separated in real time during the sampling progress by using this criterion.Furthermore,the orthogonality and completeness of the observation matrix(which is build by the illumination patterns)can obviously affect the quality of the reconstructed image.Thus,a criterion based on the orthogonality of observation matrix is proposed to judge the imaging quality of ghost imaging schemes which using different kind of illumination patterns.In this section,the imaging schemes which using different kinds of illumination patterns are discussed and compared,the results suggest that,without external influences,the imaging quality of imaging schemes with ordered illumination patterns is significantly better than schemes with random illumination patterns.In the aspect of external factors,the influence of the free propagation of light beam(from the light source to the target object)is considered,the distortion on the reconstructed image caused by diffraction is discussed,and a comparison of schemes using different illuminating patterns is made.According to the results,the scheme with random illumination has a higher robustness to the effects of diffraction.The influences of the coherence in the light source on the imaging quality are also studied.As another important result,by partially destroying the coherence of the coherent light source,the resistance of ghost imaging system on the diffraction of light can be significantly improved.Both the field of view and the spatial resolution can be improved.On the other hand,compared with the natural incoherent light,by using the artificial partly coherent light as the light source of ghost imaging,the effective distance of imaging can be further.The reconstruct algorithm based on the pseudo-inverse of the observation matrix is also discussed,by using this algorithm to reconstruct the image of the object,the distortion caused by the propagation can be completely neutralized,however,the imaging scheme based this algorithm does not work well with external noise.Furthermore,the influences of external Gaussian noise,the property of spatial light modulation devices and the manual operation on the imaging quality are also investigated.As another important result,it is found that it is possible to realize the imaging of an occluded object,once the condition which the distance between the obstacle and the target is far enough is satisfied,even if the shape and the size of the obstacle is completely unknown.The factors studied in this dissertation is widely existed in the practical applications of ghost imaging technique.This dissertation is of great theoretical value and has guiding significance in improving the quality of ghost imaging technique,it also has positive significance in the practical application of ghost imaging technique.Moreover,the criterions proposed in this dissertation have strong practicality in improving the imaging quality and judging the imaging quality of different ghost imaging techniques.Furthermore,in this dissertation,we theoretically proved that,by using ghost imaging technique,the image of an occluded object can be obtained,there is no doubt that,this will be very useful in practical applications.