The Quality Of Ghost Imaging In Homogeneous Medium

Correlated imaging,also known as “ghost imaging” or “quantum imaging”,is a novel imaging method.It can achieve nonlocalized imaging,and has been widely concerned in recent years.At present,the research of ghost imaging is mainly carried out in the atmosphere.Because the refractive index of the air is relatively small,so the effect on the quality of ghost imaging is very small.There are a lot of media with high refractive index,which are common in optical fiber and water in transparent liquid.In this paper,based on the basic theory of correlated imaging,the quality of ghost imaging in homogeneous media has been deep studied.The specific content and innovation of this paper are listed as follows:1.Based on classical temporally incoherent non-stationary pulsed light,we establish the theoretical model of temporal ghost imaging system over optical fiber and research on the principle of temporal ghost imaging over optical fiber.Based on the intensity fluctuation correlation function,the analytical expression describing the point spread function of temporal ghost imaging over optical fiber is firstly derived.It is found that there is a close relationship between the quality of temporal ghost imaging over optical fiber and the optical fiber length,group-velocity dispersion coefficient,effective width of the incident pulse.It is important that one needs to quantitatively evaluate the performance of an imaging system for designing a practical imaging system.Here we use fidelity to analyze the quality of temporal ghost imaging over optical fiber,which characterizes the similarity between the image obtained from the realistic imaging system and the ideal imaging pattern.The numerical simulation results show that the longer the optical fiber length is,the larger the group-velocity dispersion coefficient is,the smaller the effective width of the incident pulse is,the worse the quality of temporal ghost imaging is,which validates our theoretical analysis.2.By using fully spatially incoherent light,we establish the theoretical model of ghost imaging in transparent liquid.Based on diffraction theory,the impulse response function of reference arm and test arm is given.According to the intensity fluctuation correlation function,the analytical expression describing the point spread function of ghost imaging in transparent liquid is derived.We theoretically study the effects from water depth,refractive index of the medium and object position on the quality of ghost imaging system in transparent liquid.First,when the medium is water,the results clearly show that the noise increases and the resolution decreases with the increase of water depth for ghost imaging system in transparent liquid which means that a smaller water depth can provide a better imaging quality.Then,we discuss the effects from refractive index of the medium on ghost imaging in transparent liquid.We choose the air,water and carbon disulfide as the medium.According to simulation results,we can find that the noise of ghost imaging increases and the resolution reduces with the increase of refractive index of the medium.Finally,we focus on the effects from object position with water depth unchanged.We find that the noise of ghost imaging in transparent liquid is the largest with the double-slit located in the middle of the water,compared with the situation of a double-slit located in the bottom and top of the water.These may be helpful for the further study of underwater ghost imaging.