Wang Fei, Yang Zhaohui, Chen Yahong, Korotkova Olga, Cai Yangjian
Opt Lett. 2022 Jun 1;47(11):2826-2829. doi: 10.1364/OL.460911.
The coherence-orbital angular momentum (COAM) matrix characterizes the second-order field correlations in stationary sources or fields, at a pair of spiral modes with the same or different topological charges, say l and m, and at a pair of radial positions. In this Letter, we reveal the general properties of the COAM matrix for the broad class of the Schell-model sources with circularly symmetric spectral densities. Our results imply that the structure of the COAM matrix is intimately related to the symmetries of the degree of coherence (DOC). In particular, the COAM matrix is diagonal if the DOC is real-valued and rotationally symmetric; otherwise, it may acquire non-zero off diagonal elements. In particular, if the real part of the DOC has Cartesian symmetry, the COAM matrix's elements with the even/odd index difference |l - m| contain information about the real/imaginary part of the DOC. A potential application of our results is envisioned for extracting the rotation angle of the DOC of light (or an object transparency) through measuring of the off-axis COAM matrix elements.
相干轨道角动量（COAM）矩阵表征了静止源或场中二阶场相关性，涉及一对具有相同或不同拓扑电荷（设为l和m）的螺旋模式以及一对径向位置。在本信函中，我们揭示了具有圆对称光谱密度的广义Schell模型源的COAM矩阵的一般性质。我们的结果表明，COAM矩阵的结构与相干度（DOC）的对称性密切相关。特别地，如果DOC是实值且旋转对称的，则COAM矩阵是对角的；否则，它可能具有非零的非对角元素。具体而言，如果DOC的实部具有笛卡尔对称性，则具有偶数/奇数索引差|l - m|的COAM矩阵元素包含有关DOC实部/虚部的信息。我们的结果的一个潜在应用是设想通过测量离轴COAM矩阵元素来提取光的DOC的旋转角度（或物体透明度）。
