Research On Multidimensional Information Measurement And Performance Improvment Of Ghost Imaging System

In the past twenty years,ghost imaging has gained great development.When ghost imaging appeared for the first time,it is considered as nonlocal quantum correlations between the photon pairs.And then it was proven that ghost imaging could be also achieved by utlizing pseudo-thermal light.This dicovery drives ghost imaging forward into the future.Comparing with other imaging methods,ghost imaging with pseudo-thermal light as source has many advantages,such as wide working waveband,long detection range,realizing the miniaturization easily,powerful adaptability for complex detecting condition.Ghost imaging become a hotspot in the field of lidar and remote sensing area for its s trong ability to resist atmospheric turbulence and free from Rayleigh diffraction limit.However,ghost imaging system is still with single function even now.Many researchers focus on improving the algorithm of ghost imaging,and ignore how to change ghost imaging system to broaden its application.Hence,most research about ghost imaging are how to obtain high quality intensity images,and measurement of object 's other dimensions information have been overlooked.However,there still be several problems in ghost imaging system.These problems contain that imaging speed of 2D ghost imaging is slow,image resolution of 2D ghost imaging decreases owe to atmosphere turbulence,and range accuracy of 3D ghost imaging is at low level.These problems greatly restrained the application and development of lidar based on ghost imaging.In addition,target information which can be measured by ghost imaging system lacks variety.Only intensity and range information can be obtained by ghost imaging system.The whole target information can not be gained through these two dimensio n informations under complex detection circumstance.It needs to measure multi-dimension information through ghost imaging system,such as the dimension of polarization.Therefore,it is necessary to research how to improve performance of ghost imaging sys tem and expand range of ghost imaging system measuable information from two-dimension and three-dimension to multi-dimension information.In this paper,which factors can influence image resolution of 2D ghost imaging system under atmosphere turbulence are analyzed,and imaging formula is also derived with help of Fresnel diffraction integral formula.And then,Gaussion beam,which is used as source in conventional ghost imaging system,is replaced by hyperbolic cosine Gaussian(HCG)beam in order to improve imaging resolution.Through numerical simulation,it is proved that imaging resolution of ghost imaging system with HCG beam is better than that with Gaussion beam.At last,multi-wavelength ghost imaging(MWGI)system is proposed to improve the imaging speed.Source of the system is a multi-wavelength beam and different wavelength beams in source are modulated by different methods.With this kind of source,MWGI system can obtain sampling data in unit time.Therefore,MWGI system can reconstruct intensity images with high speed.Experiment is also performed and experiment results demonstrated the effectiveness of MWGI system.For the range accuarcy of 3D ghost imaging,we analyze the relationship between slicing number with range accuracy based on ghost imaging range and range accuracy formulation with centroid method.Through the analysis,we find that simply increasing slicing number will decrease range accuracy.There is an optimum slicing number.When the slicing number is above this slicing number,th e influence of the noise becomes more and more intense.We propose a 3D ghost imaging system with optimum slicing number(OSN)method and perform a 3D ghost imaging experiment based on OSN method.A wall located at 180 m away is chosen as the target,and range image of the target is obtained with conventional 3D ghost imaging method,centroid method,and OSN method respectivly.We utilize root-mean-square error(RMSE)to envalue range accuracy.For low range resolution of 3D ghost imaging under low sampling rate of data acquired system,we propose a heterodyne 3D ghost imaging which obtains range information of target through heterodyne method.This system utilizes a continuous wave laser as source.Light intensity is modified by an electro-optical crystal.After intensity modification,a spatial light modulator(SLM)is used to modify speckle distribution.A bucket detector receives echo light from targets.Target range information can be obtained by temporal correlation calculation of recorded intensity and modified signals on the electro-optical crystal.Through spatial correlation of speckle distribution and echo light intensity from targets,target intensity information can be calculated.Range resolution of HGI system is also analyzed,and it can be concluded that range resolution of HGI is not influenced by sampling rate of data acquiring system.Simulation results show that under same sampling rate condition,range resolution of HGI is better than that of convetional 3D ghost imaging system.In order to identify different materical targets with same reflectivity,this work proposes a polarization ghost imaging system to obtain the polarization image.The polarization ghost imaging system is used to measure the polarization state distribution reflected from target through ghost imaging method and gives polarization image of target.A polarized chromatic value(PCV)is introduced.The PCV is described as the spatical polarization distribution of the reflected light from the target.Simulation results demonstrate that polarization ghost imaging system can obtain polarization image of target which can be utilized to distinguish different materials target with same reflectivity.