为探究Bragg光栅结构对TM模反馈特性的影响，利用有限时域差分法对具有TM模的分布反馈（DFB）量子级联激光器Bragg光栅结构进行仿真研究。重点分析了侧向耦合光栅的光学特性以及光栅侧壁倾角对光栅反射谱、损耗的影响及原因，并探究了光栅刻蚀深度及占空比与TM模的耦合系数、损耗的关系。结果表明有效折射率是影响Bragg波长的主要因素，而光限制因子是不同周期的侧向耦合光栅结构耦合系数产生巨大差别的原因，当光栅侧壁倾角90°时镜面损耗最小。光栅周期、占空比、刻蚀深度与耦合系数的关系表明：这些参数不仅影响光栅的相对介电常数，也会对光限制因子产生作用，从而影响耦合系数的大小；耦合系数与刻蚀深度具有正比关系，大周期光栅耦合系数随占空比的变化率较小。对光栅光反馈特性的理论研究有利于提升对DFB量子级联激光器的认识，促进激光器性能的提升和发展。

掺镱光纤是高功率激光器的核心材料，但在高能射线辐照后其应用性能会显著下降，因此有必要对掺镱光纤材料在辐照环境下的性能变化进行深入研究。采用改进型化学气相沉积法结合稀土螯合物掺杂制备了系列光纤预制棒及光纤，测试了光纤在不同剂量下射线辐照前后的高功率输出性能，以及光纤预制棒辐照前后的吸收光谱及镱离子荧光寿命。结果表明：小剂量辐照后掺镱光纤的高功率输出显著下降，通过预制棒吸收光谱可看出主要是因为伽马辐照后使掺镱光纤材料中Al的相关缺陷浓度增多，在可见光区域吸收损耗增加。Ce离子的掺杂通过缓减辐致铝氧空位中心（Al-OHC）色心缺陷的增加，减少Yb离子荧光寿命的下降，可在一定程度上抑制高功率掺镱光纤的辐致暗化。

We demonstrate high-resolution and high-quality terahertz (THz) in-line digital holography based on the synthetic aperture method. The setup is built on a self-developed THz quantum cascade laser, and a lateral resolution better than 70 μm (～λ) is achieved at 4.3 THz. To correct intensity differences between sub-holograms before aperture stitching, a practical algorithm with global optimization is proposed. To address the twin-image problem for in-line holography, a sparsity-based phase retrieval algorithm is applied to perform the high-quality reconstruction. Furthermore, a new autofocusing criterion termed “reconstruction objective function” is introduced to obtain the best in-focus reconstruction distance, so the autofocusing procedure and the reconstruction are unified within the same framework. Both simulation and experiment prove its accuracy and robustness. Note that all the methods proposed here can be applied to other wavebands as well. We demonstrate the success of this THz synthetic aperture in-line holography on biological and semiconductor samples, showing its potential applications in bioimaging and materials analysis.

Beryllium carbide (Be₂C) thin films have proven to be promising ablation materials, but the properties of Be₂C coatings of the greater thickness required for inertial confinement fusion capsules are still unknown. In this work, Be₂C coatings of various thicknesses (0.3–32.9 μm) are prepared by DC reactive magnetron sputtering. The influence of thickness on crystal properties, microstructure, and optical properties is investigated. The results indicate that the crystallinity of polycrystalline Be₂C films improves with increasing thickness, while the grain size (～5 nm) and texture properties (without a preferred orientation) have only a weak dependence on thickness. A uniform featureless microstructure and smooth surface (root mean square roughness ～8 nm) are observed even in thick (32.9 μm) films, despite the presence of defects induced by contaminants. High densities (2.19–2.31 g/cm³) and high deposition rates (～270 nm/h) are realized, with the latter corresponding to the upper limit for the fabrication of Be₂C coatings by magnetron sputtering. The transmittance of the films in the near-infrared region remains at a high level (>80%) and has only a weak dependence on thickness, while the transmittance in the visible region decreases with increasing thickness. In addition, the optical bandgap is estimated to be about 1.9 eV and decreases with increasing thickness owing to the presence of defects.