Propagation properties of a partially coherent electromagnetic hyperbolic-sine-Gaussian vortex beam through anisotropic atmospheric turbulence.

Using the extended Huygens-Fresnel principle and the Rytov approximation, the analytical formula for the propagation of a partially coherent electromagnetic hyperbolic-sine-Gaussian vortex beam (PCEShVB) in anisotropic atmospheric turbulence has been theoretically derived. Detailed studies have been conducted on the evolution characteristics of the average intensity, the degree of coherence (DOC), and the degree of polarization (DOP) of the beam in turbulence. The results show that during propagation, the intensity distribution of the beam will exhibit a spiral structure, and the overall distribution of the light spots will rotate in a direction related to the sign of the topological charge. The DOC distribution of PCEShVB will display a pattern reminiscent of beam interference fringes with an increase in propagation distance, with the number of "interference fringes" greatly impacted by the hyperbolic sine parameter. Furthermore, PCEShVB with a large initial coherent length and hyperbolic sine parameter will increase the degree of separation of the spots and yield a large DOP. Finally, for the validation of the theoretical findings, the random phase screen method was employed to simulate the propagation of PCEShVB through anisotropic atmospheric turbulence. The studies revealed a consistent alignment between the simulation results and the theoretical predictions.

Light curve measurements with a superconducting nanowire single-photon detector.

The superconducting nanowire single-photon detector (SNSPD) is used to detect the sunlight reflected by the artificial satellite and space debris. In the process, light curves of the satellite and space debris are successfully measured. In 2017, a space-debris laser ranging system with a four-element SNSPD is developed by Yunnan Observatories in China. During the ranging experiments, the detector works in a freely detecting state. It can detect photons not only of the laser echo, but also of the sunlight reflected by the target. After separating the data triggered by background light from the whole detected data set, the light curves of satellites, including Topex and several types of debris, are acquired. The apparent rotation rate of the satellite Topex is determined by analyzing the light curves by Fourier transform and phase dispersion minimization. On the basis of a laser ranging system using SNSPDs, the simultaneous measurement of the laser ranging and light curves of some space targets without any additional equipment is realized for the first time, to the best of our knowledge.