极弱光关联成像研究进展及展望（特邀）

光学成像因其分辨率高，信息量丰富，具有其他探测和感知技术不可替代的地位，是人们获取信息最重要的技术手段之一。光子是光学成像系统中的信息载体。光学图像的高质量重构，依赖于对信号光子的高效耦合和对光信息的精准解耦。然而，在遥感或生物成像等重要应用场景中，由于作用距离远或辐照功率低，到达探测面的物体信号光子数少，信噪比低，对光学系统设计、信号探测和图像恢复都带来了极大困难，严重限制了光学成像性能。如何在极弱光条件下获得高质量图像，是光电成像系统研究的基础性难题，也是推动光学成像不断向更大视场、更远作用距离、更高信息通量发展亟待克服的关键技术。近年来，在光场调控和量子探测技术支撑下，并基于光场的高阶经典/量子关联发展起来的关联成像，由于探测灵敏度高、抗干扰能力强，为发展极弱光条件下的光学成像技术带来了新的机遇。文中将简要回顾关联成像的原理机制，在此基础上系统介绍极弱光条件下关联成像方案和方法。并尝试从光子动力学层面解释这些方法的物理本质，讨论这些方法的能力极限，比较这些方法所适用的场景。

Progress and prospect of ghost imaging in extremely weak light (Invited)

Possessing high resolution and rich information, optical imaging is one of the most important techniques for people to obtain information. Photons are information carriers in optical imaging systems. The high-quality reconstruction of optical image depends on the efficient coupling of signal photons and the accurate decoupling of optical information. However, in important application scenarios such as remote sensing or biological imaging, due to the long operating distance or low radiation power, the number of signal photons from the object to the detection plane is small, and the signal-to-noise ratio is low, thus bringing great difficulties to the design of optical system, the signal detection and the image reconstruction, and seriously limiting the performance of optical imaging. How to obtain high-quality images under extremely weak light conditions is not only a basic problem of photoelectric imaging system research, but also a key technology to promote the vigorous development of optical imaging with a larger field of view, longer working distance and higher information flux. In recent years, with the support of light field modulation and quantum detection technology, and based on the high-order classical/quantum correlation of light field, ghost imaging has brought new opportunities for the development of optical imaging technology under extremely weak light conditions, due to its high detection sensitivity and strong ability against interference. This paper briefly reviewed the principle and mechanism of ghost imaging, and systematically introduced the schemes and methods of ghost imaging under very weak light conditions. The physical essence of these methods from the level of photon dynamics was introduced, the capability limits of these methods were discussed, and the applicable scenarios of these methods were compared.