Research On Ghost Imaging For Application In Complex Scenarios

Ghost imaging is a technology in which the information of the object is acquired based on the high-order coherence of the light field.Compared with conventional imaging,ghost imaging possesses advantages in some aspects.Firstly,lensless imaging can be achieved via ghost imaging.This makes imaging easier at some operation wavelength,such as X-ray,in which spectrum lens is hard to get.Secondly,in ghost imaging,the information of a 2-or 3-dimension object can be obtained with a single-pixel detector.Compared with a common array sensor,the sensitivity of single pixel is higer,thus ghost imaging can provide images with extremely weak illumination.Besides,the read\write speed of a single-pixel detector is fast.This makes the the data acquiring process of ghost imaging fast.In addition,due to the way of information acquiring based on the correlation of the intensity of the light field,the noise which is independent on the light field will be suppressed or even dismissed.Last but not least,Compressive sensing or machine learning can be introduced in ghost imaging to improve the quality of the image.A large number of samplings are required to obtain the information of the objects,thus limits the performance of ghost imaging in imaging moving objects.Besides,the non-uniform statistical distribution of the illumination field and the phase noise in the system have influence on the quality of the reconstructed image.In order to improve the adaptability of correlation imaging in application in complex scenarios and bring the advantages of ghost imaging into practice,in this paper,we study and analyze the influence of non-uniform light source,motion of object,atmospheric turbulence and other factors on the quality of the reconstructed image in ghost imaging,then we propose schemes to improve the performance of ghost imaging.This paper is organized are as follows:Firstly,an algorithm with normalizing second-order coherence of the light field is proposed.The point spread function(PSF)in ghost imaging is analyzed,and the influence of non-uniform second-order coherence and power fluctuation of the laser on the quality of ghost imaging is studied.By normalizing the PSF in the imaging system,our method can effectively suppress the statistical noise caused by limited sampling or power fluctuation of the laser.Under the condition with non-uniform illumination field,the image quality of our method is higher than that from differential correlation algorithm.Thus,the robustness of correlation imaging to imperfect light source is improved.Secondly,temporal differential ghost imaging scheme is proposed.The scenario that object is moving in complex background is considered and the requirement on the parameters of the imaging system for ghost imaging in this situation are analyzed.Based on the characteristics that the background is static and the moving objects in the scene is sparse,the same speckle sequence is used to illuminate the scene at different times.Then the difference of the signals from bucket detector is calculated and then correlated with the distribution of the illumination field.In this way,the influence of the static background is subtracted,the number of samples required for moving object imaging is reduced,and the ability of the Ghost imaging system to image the moving objects in the complex scene is improved.Thirdly,tracking and imaging based on the object autocorrelation is proposed.The correlation of the temporal information of moving objects is studied.This paper find that less number of samplings are required to obtain the motion information of the object than that to obtain the image of the object.Based on this fact,the moving object is tracked based on cross correlation,then the image can be obtained during its evolution process.The requirement on sampling rate of the system in Ghost imaging is reduced.It improves the ability of Ghost imaging in tracking and imaging moving objects with high-speed.Finally,computational ghost imaging with the phase difference is proposed.The influence of phase noise on ghost imaging system is analyzed.When there is random phase noise in the source plane of ghost imaging,the point spread function of the ghost imaging system is the spectrum of the phase noise,and the image of the object cannot be directly obtained from the results of the second-order intensity correlation.The image of the object can be reconstructed from the autocorrelation of intensity correlation results with a phase retrieve algorithm.Our method can still obtain the image of the object when the phase noise on the light source is greater than 2 pi.Moreover,our method possesses the posibible to improve the robustness of ghost imaging against turbulence.In addition,we quantitatively analyzed the influencing factors of imaging quality in this method.The influence of the parameters of imaging system on the quality of the reconstructed image is discussed.