In this paper, we propose an ultrabroadband chiral metasurface (CMS) composed of S-shaped resonator structures situated between two twisted subwavelength gratings and dielectric substrate. This innovative structure enables ultrabroadband and high-efficiency linear polarization (LP) conversion, as well as asymmetric transmission (AT) effect in the microwave region. The enhanced interference effect of the Fabry–Perot-like resonance cavity greatly expands the bandwidth and efficiency of LP conversion and AT effect. Through numerical simulations, it has been revealed that the cross-polarization transmission coefficients for normal forward (-z) and backward (+z) incidence exceed 0.8 in the frequency range of 4.13 to 17.34 GHz, accompanied by a polarization conversion ratio of over 99%. Furthermore, our microwave experimental results validate the consistency among simulation, theory, and measurement. Additionally, we elucidate the distinct characteristics of ultrabroadband LP conversion and significant AT effect through analysis of polarization azimuth rotation and ellipticity angles, total transmittance, AT coefficient, and electric field distribution. The proposed CMS structure shows excellent polarization conversion properties via AT effect and has potential applications in areas such as radar, remote sensing, and satellite communication.

In this paper, the frequency difference of the eigen polarization modes of the Nd:YAG crystal laser at different polarization ratios is experimentally studied, and to the best of our knowledge, the correlation between the frequency difference of the eigenmodes and the output polarization degree is reported for the first time. Combined with the analysis of the polarization beam profile, it is proved that the polarized laser produced by the isotropic crystal is due to the frequency locking of the eigen polarization modes. The weak birefringence in the crystal causes the round-trip phase difference of the orthogonal polarization modes, which leads to the frequency difference between the polarization modes. By the adjustment of the cavity mirror, the anisotropic loss will interact with the round-trip phase difference. The eigen polarization modes can reach frequency degeneration, and then be coherently combined to produce linearly polarized laser output. This work provides a useful reference for understanding the physical mechanism of polarized lasers realized by isotropic crystals.

为了使2.16 m望远镜具备线偏振测光观测能力，开展了偏振光度计研制。该系统采用双通道分时偏振成像方案，具有偏振定标单元、偏振测量单元，可实现偏振定标、偏振测量和多色测光。完成系统研制后，将其安装在2.16 m望远镜上开展实测，依照该偏振光度计偏振观测流程拍摄了一系列非偏振标准星、偏振标准星、流量标准星；按照偏振定标和偏振态解算数据处理方法，对获取图像进行数据处理。结果显示：该偏振光度计视场为4.63′×4.63′，像元比例尺为0.54 (″)/pixel，偏振度测量精度优于0.01，60 s曝光时间可以拍摄到V波段信噪比约为141的15.3等星。该偏振光度计使2.16 m望远镜具备V波段线偏振测光和快速多色测光观测能力。

近年来，因为体现出诸多异常拓扑现象，外尔超材料一直备受关注。此前的研究表明外尔超材料的反射场具有偏振转换特性。然而，关于反射本征态的讨论却不够深入，原因在于入射电磁场与反射电磁场处于不同的态空间，给分析计算带来了诸多不便。文中从电场为极矢量、磁场为轴矢量的基本特性出发，通过引入镜像算符将入射态空间与反射态空间联系起来，最后对全反射界面的本征态进行了明确的定义。依据上述定义，笔者对外尔超材料的反射本征态进行了计算，结果显示：在入射电磁场为线性偏振的前提下，外尔超材料的反射本征态均为线性偏振态。反射本征态为线性偏振态，这一性质是由系统能量守恒与洛伦兹互易性共同保证的。经过进一步探讨发现，当动量空间的路径绕外尔点一圈时，本征态的电磁场方向旋转角度为90°。这也意味着如果电磁场要回到初始状态，动量空间的路径需绕外尔点4圈。这一现象的拓扑结构可以类比为四阶莫比乌斯环。此外，依据反射本征态为互相垂直的线性偏振态这一特性，笔者定义了旋转角度θ用以描述本征态朝向的变化规律。值得一提的是，这种计算方法不仅仅适用于外尔超材料，满足条件的全反射界面的反射本征态均可以依照上述定义与方法进行分析求解。

红外偏振成像技术具有探测距离远，目标识别率高等多种优势，但在复杂环境下目标偏振特性易受背景辐射影响，使得红外偏振设备的探测能力大幅降低。本文基于偏振双向反射分布函数，综合考虑目标和背景间的辐射耦合效应，建立了目标偏振度计算模型。对比研究了有强辐射背板和无强辐射背板两种情况下目标偏振度的变化情况，并针对陆基和机载探测等小角度探测情况，仿真研究了目标和背板的温度、夹角等参数对目标偏振度的影响规律。研究结果表明：目标和背板温度相同时，辐射耦合效应会显著降低目标的偏振度，但不会改变目标偏振度随温度升高而增大的趋势。当目标和背板温度为30 °C、40 °C和50 °C时，目标偏振度的最大值分别为无强辐射背板时的63.7%、44.9%和42.2%。可见温度越高，目标和背板间的辐射耦合效应越强，目标偏振度降低的比例越大。此外，辐射耦合效应的强弱不仅与温度有关，还与目标和背板的夹角有关。随着夹角的增大，目标偏振度先增大后减小，且在夹角约为105°处取得极大值。因此，辐射耦合效应会在一定程度上改变目标偏振度，从而影响红外偏振设备的探测能力。最后，通过搭建的长波红外偏振成像系统，对建立的目标偏振度计算模型进行了实验验证，实验结果与仿真分析结果基本一致。本文研究成果对提升陆基和机载红外偏振设备的探测和识别能力具有一定的指导意义。