| As we all know,traditional optical imaging is highly susceptible to the surrounding conditions and imaging distance.In response to this situation,a new type of imaging method was derived under the combination of quantum physics and imaging technology in the 1980 s,that is,active illumin ation correlation imaging,also known as ghost imaging.The difference from traditional optical imaging is that it does not use the detector to directly image the object,but reconstructs the target image in the optical path without the object through the second-order or high-order correlation method.In the imaging process,the b ucket detector that receives the light passing through the object only counts the light intensity value,and does not need to perform spatial resolution measurement,and the other beam associated with it is freely transmitted in space.As long as the imaging distance requirements are met,the corresponding object image or Fourier diffraction pattern of the object can be recovered.Therefore,ghost imaging has non-locality and anti-interference characteristics,and can even reconstruct high-resolution images in low-light environments.In traditional optical imaging,factors such as angle of view,target characteristics,and distance all have a certain impact on imaging quality,especi ally when the measurement orientation deviates from the object or the target to be measured rotates at high speeds,it will be difficult to obtain a clear image of the object.Under the constraints of these conditions,whether ghost imaging can use its special advantages to expand the effectiv e imaging measurement range,overcome the negative effects of object rotation,and maintain the stable state of the reconstructed image during long-distance detection are issues that we need to explore.And judging from the current research status,most of the relevant researches have stayed in theoretical analysis,especially for rough objects,the experimental results are scarce.Therefore,based on the reflective target,this article explores the effects of imaging angle,object surface characteristics,target rotation,and imaging distance on ghost imaging in theory and experiments.The main results are summarized as follows:(1)First,it reveals that the ghost imaging system can effectively expand the effective imaging measurement range of the target o bject,and solves the problem of blind area in active illumination imaging when the light source is incident at a large angle.Theoretically,based on the Huygens-Fresnel diffraction integral formula and the paraxial approximation conditions,the intensity fluctuation correlation function model of the reflective ghost imaging system with a smooth object is established,and the point spread function expression is obtained from it.By comparing the point spread function of the traditional optical imaging system,it is found that the image resolution corresponding to the ghost imaging system is higher at the same incident angle.Experimentally,double slits with a slit width of 0.2 mm and a slit spacing of0.8 mm are used as the imaging target.When the incident angle of the light source on the surface of the object reaches 5?/12,the active illumination imaging can no longer resolve the double slits information,and the correlation imaging can reconstruct a double-slit image with better resolution even after the b ucket detector's lateral measurement range is reduced to one pixel.(2)Second,according to the relationship between the surface height fluctuation of the object and the change of the amplitude of the scattered wav e,a theoretical model of ghost imaging with rough objects is established,and the theoretical system of correlation imaging based on amplitude and phase objects is improved on the basis of the amplitude object.At the same time,objects with different sur face characteristics are selected as imaging targets,and the changes in imaging resolution and signal-to-noise ratio are experimentally explored.It is clear that the roughness of the surface of the object and the lateral size of the b ucket detector have no effect on the imaging resolution.And the signal-to-noise ratio of the image will be better when using low-roughness objects and small-sized bucket detectors and keeping the light source at a large reflection angle.(3)In view of the situation that the rotation of the imaging target will cause image blur in traditional optical imaging,combined with the imaging results of the ghost imaging system at the above-mentioned large angle,the ability of the imaging system to reconstruct the Fourier image of th e object under different angles of view of the object and the rotation of the target is studied.It is confirmed that compared with the ghost diffraction system,the HBT system is more resistant to the rotation of the object around the axis,and reconstructs a relatively standard Fourier image when t he detector is close to the object.(4)Using the optical transmission matrix to characterize the key parameters of the impulse response function in complex optical systems,the imaging theoretical models of the lensless ghost diffraction system and the le nsed ghost diffraction system are established,and clarify the unified imaging conditions between different ghost diffraction systems in the far field environment.In the experiment,by setting the difference between the distance from the light source to t he CCD detector and the distance from the light source to the imaging target as the far field,the changes of the Fourier image recovered by the system when the point detector is in the near field and far field of the object plane are studied.It is confirmed that as long as the difference between the free transmission distance of the beam in the reference optical path and the transmission distance of the beam in front of the object and the position of the point detector are in the far field range,the ghost diffraction system can reconstruct the Fourier image with good quality in the presence of defocusing. |
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