Higher-order Correlated Imaging With Thermal Light And Visibility

Correlated imaging, which is also named coincidence imaging or ghost imaging, is a completely new theory of imaging deriving from quantum theory. The peculiar characters arising from correlated imaging have become one of the central topics in quantum optics in recent years. Initially, the possibility of performing correlated imaging was ascribed to the presence of spatial entanglement between the two systems. It was claimed that quantum entanglement was a crucial prerequisite for achieving ghost imaging. Lately this view has been challenged from both theoretical and experimental aspects. It has been shown that classical correlation can play the same or similar role as quantum entanglement. A thermal or quasi-thermal source can exhibit such classical correlation. So we can realize correlated imaging with thermal or quasi-thermal light. Correlated imaging using classical thermal light provides us with an experimental basis for its application in other areas, such as quantum eraser, quantum cryptography, quantum holography, phase-conjugate mirror and so on.In this thesis, we propose a ghost imaging scheme with higher-order correlated thermal light, derived the Gaussian thin lens equations, and calculated the N-order correlation function of our optic system. Our scheme consists of N linear optical systems: one test system and N-1 reference systems. An object is placed in the test system, furthermore, a collection lens and a collection detector are also located in it. The N-1 reference systems include a imaging lens and a scanning detector respectively. After the thermal source, a combination of many beam splitters splits the radiation into N distinct optical paths. The detectors receive the optical signals and conversion it to electrical pulses, then sent it to an electronic coincidence circuit to measure the rate of coincidence counts. From the correlation function we can see that if the Gaussian thin lens equations are satisfied, the information about the object will be recreated nonlocally from the spatial correlation function between the test and reference system in a nonlocal fashion. In other words, it is possible to produce N-1 ghost images at N-1 different places from one object. Our present scheme is a many-ghost imaging protocol. It opens up new avenues for realizing multi-port information processing. The appearance of the many ghost images reveals an observable physical effect of higher-order coherence or correlation of optical fields. Hence, it is of very significance to study higher-order correlated imaging not only for well understanding the essential physics behind the higher coherence or correlation of optical fields but also for developing multi-port information processing technology.We have investigated the geometrical optics in fourth-order correlated imaging system, analyzed the real ghost image and virtual ghost image in eight different cases, and obtained the propagation geometrics of the light.Furthermore, we have investigated the visibility of the ghost images. According to the correlation function, we obtained the visibility expressions of second-order and higher-order correlated ghost imaging, and calculated their maximum respectively. The results show that the source, the object and the correlation-orders will all have influence on the visibility of the ghost image, and the bigger numbers of correlation-order, the better visibility.