Polarizers have always been an important optical component for optical engineering and have played an indispensable part of polarization imaging systems. Metasurface polarizers provide an excellent platform to achieve miniaturization, high resolution, and low cost of polarization imaging systems. Here, we proposed freeform metasurface polarizers derived by adjoint-based inverse design of a full-Jones matrix with gradient-descent optimization. We designed multiple freeform polarizers with different filtered states of polarization (SOPs), including circular polarizers, elliptical polarizers, and linear polarizers that could cover the full Poincaré sphere. Note that near-unitary polarization dichroism and the ultrahigh polarization extinction ratio (ER) reaching 50 dB were achieved for optimized circular polarizers. The multiple freeform polarizers with filtered polarization state locating at four vertices of an inscribed regular tetrahedron of the Poincaré sphere are designed to form a full-Stokes parameters micropolarizer array. Our work provides a novel approach, we believe, for the design of meta-polarizers that may have potential applications in polarization imaging, polarization detection, and communication.

Er³⁺和Yb³⁺共掺杂的YAG晶体是一种非常重要的光学晶体, 目前, 该晶体已经广泛应用于高功率固体激光器, 但是采用提拉法生长大尺寸、低缺陷的掺杂YAG晶体仍然面临很多挑战。本工作采用快速提拉法成功获得了直径为80 mm、长度为230 mm的Er³⁺和Yb³⁺共掺杂的YAG单晶。采用不同测试方法评价其结构、掺杂浓度、光吸收、发光性能和刻蚀缺陷。晶片不同位置的拉曼峰峰位以及半峰宽没有明显变化, 说明晶片中心和边缘部分的晶体结构和应变是均匀的。刻蚀结果表明, 腐蚀坑均匀分布在整个腐蚀表面上, 没有观察到位错腐蚀坑特征, 这意味着晶体接近完美。Er³⁺和Yb³⁺在不同波长下的强发光峰以及辉光放电质谱结果证明Er,Yb:YAG单晶中成功掺杂了稀土离子。本工作采用提拉法成功生长了大尺寸、低缺陷的Er,Yb:YAG单晶, 证实了快速生长方法对YAG晶体中掺杂双稀土离子是有效的。