Analysis Of Imaging Quality In Different Ghost Imaging Systems Using Coherent-mode Representation

Correlated imaging,also known as ghost imaging,has made great progress in the past few decades and has important significance in theory and practice.Different from traditional imaging,correlated imaging is a nonlocal imaging technique,i.e.,ghost-image is generated on the optical path that does not contain the object imaged.The intensity fluctuation correlation function between detectors in two paths contains the information of the object,which is used to reconstruct the ghost-image or Fourier-transform image.The coherent-mode representation theory is particularly suitable for evaluating the imaging quality and retrieving the unknown information.In this paper,we mainly analyze the imaging quality of ghost microscope imaging system and the influence of defocusing on imaging quality based on the coherent-mode representation theory,and the difference of imaging quality between different imaging systems is studied by this method.Firstly,the applicability of coherent-mode representation theory in ghost microscope imaging system is discussed.The present theory on classical correlated imaging is based on the integral representation,which have been derived from both quantum optics and statistical optics.In the second-order coherence theory of optical fields,it is well known that the cross-spectral density function of the source can be decomposed into a linear superposition of a series of coherent modes.The coherent-mode representation of the second-order intensity fluctuation correlation function between two detectors and object function are derived by means of the coherent-mode representation of the source.It is shown that the ghost-image quality depends crucially on the distribution of the eigenvalues and the decomposition coefficients of the objects.If the distribution of the eigenvalues is wider than the distribution of the decomposition coefficients of the objects,one can obtain high quality ghost images.Otherwise,the ghost images will be significantly degraded.In other words,when the distribution of the eigenvalues is unchanged,the narrower the distribution of the decomposition coefficients of the objects is,the better the imaging quality is.The above conclusion is verified by the experimental and numerical simulation.Secondly,the influence of defocusing effect on imaging quality of ghost microscope imaging scheme is discussed with the help of the coherent-mode representation theory.Numerical simulation and experimental results show that when there is defocusing effect in imaging system,the decomposition coefficients of the objects will become wider,then the imaging quality will get worse.Therefore,we should avoid the appearance of defocusing effect in imaging experiments.Finally,we use the coherent-mode representation theory to evaluate the difference of imaging quality between different ghost imaging schemes.when the distribution of the eigenvalues is unchanged,the narrower the distribution of the decomposition coefficients of the objects is,the better the imaging quality is.Therefore,by comparing the distribution of the decomposition coefficients of the objects one can evaluate the imaging quality between different imaging systems.It is shown that by comparing the distribution of decomposition coefficients of the objects of a new-designed imaging system with that of the existing schemes,one can know whether imaging quality of the new imaging system is better than that of the existing system.Three kinds of ghost imaging systems are chosen to verify our results.