Transmission Characteristics And Correlated Imaging With Partially Coherent Light Through Turbulent Atmosphere

When laser propagates in atmosphere, the beam parameters such as light intensity distribution, beam radius and arrival angle are seriously affected by the atmospheric turbulence. At the same time, the coherence of the laser will be destroyed and become partially coherent light. In recent years, scholars have carried out a lot of theoretical research on transmission characteristics of partially coherent light through turbulent atmosphere, and found that the scintillation index of partially coherent light is smaller than completely coherent light. But related experiments has been reported rarely. On the other hand, correlated imaging with partially coherent light which conform to thermal light fluctuation features is expected to become one of the means of target detection in the future. But, putting correlated imaging into practical application, the partially coherent light will be influenced by the atmospheric turbulence, and thus the quality of the correlate imaging would be affected. Therefore, it has important research value and practical significance for studying propagation properties of partially coherent light in atmospheric turbulence and the influence of atmospheric turbulence on correlated imaging.An analysis and a comparison of the influence on the transmission characteristics with partially coherent beam(PCB) and coherent beam(CB) is made theoretically from three aspects of optical intensity fluctuation, beam spreading and angle-of-arrival fluctuation. Emphasis is put on the experiment of PCB and CB propagating through the turbulence emulator of aqueous medium. Rytov variance of 0.4~0.16 has been generated by the turbulence emulator. Scintillation index has been obtained as a function of Rytov variance by analyzing the received intensity. The analysis shows that the scintillations indexes of PCB and CB increase with the increase of strength of turbulence, however, the scintillation index of coherent light is larger than that of partially coherent light, which is consistent with the theoretical model of Gaussian Schell beam established by Andrews et al.This paper reconstructs the amplitude-only object’s images by traditional correlated imaging algorithm and by compressive sensing algorithm, respectively. In order to investigate the influence of turbulence on imaging quality, the test arm is imbedded in the wavefront phase screen distorted by kolmogonov atmospheric turbulence thatgenerated by numerical simulation. Emphasis is put on the comparison of imaging quality with traditional correlated imaging(CI) and compressive sensing correlated imaging(CS-CI) with different turbulent level. the imaging quality decreases with the increasing level of the atmospheric turbulence. And the compressive sensing algorithm can not only reduce the number of samples, but also improve the quality of imaging significantly in free space. However, the advantage decreases with the increase in level of the atmospheric turbulence. The result indicates the intensity correlation characteristics between signal light and idle light is destroyed after turbulence affects signal light. The stronger the turbulent, the smaller the maximum of second-order correlation functions. The result indicates the imaging quality decreases with the increasing level of the atmospheric turbulence. And the compressive sensing algorithm can not only reduce the number of samples, but also improve the quality of imaging significantly in free space. However, the advantage decreases with the increase in level of the atmospheric turbulence.