Abstract ：

垂直外腔面发射激光器(VECSEL)具有高功率、高光束质量、波长可根据实际需要进行设计等独特优点,应用场景十分丰富.锁模VECSEL产生的高峰值功率脉冲能应用于多光子成像、高分辨率时域太赫兹光谱、超连续谱产生等多个重要领域.但是,半导体增益介质纳秒量级的载流子寿命,极大地限制了锁模VECSEL重复频率的降低和峰值功率的提高.使用特殊设计的可饱和布拉格反射镜(SBR)作为可饱和吸收体,其中等适度的饱和通量可以有效地平衡谐振腔内的循环功率和多脉冲的产生,从而在较低的重复频率下保持足够高的平均输出功率,显著提高脉冲的峰值功率.SBR被动锁模VECSEL的脉冲重复频率被降低到67 MHz,激光器在基波、二次谐波和四次谐波锁模状态下的脉冲峰值功率分别为2.33、3.00、1.23 kW,被动锁模VECSEL在低于100 MHz的重复频率下获得了kW量级脉冲峰值功率.另外,结合实验结果,对SBR锁模VECSEL中多脉冲的产生及谐波锁模过程的演化进行了定性的分析讨论.

Keyword ：

垂直外腔面发射激光器 被动锁模 峰值功率 重复频率

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Abstract ：

本发明公开了一种低损耗、高双折射多孔芯太赫兹光纤及制备方法，包括纤芯和包层；纤芯由基底材料以及分布在其内部的大圆形空气孔、小圆形空气孔和椭圆空气孔构成，一大圆形空气孔位于纤芯中心、剩余大圆形空气孔呈正三角形的方式沿截面竖直方向对称排列，两个椭圆空气孔水平位于中心的大圆形空气孔的左右两侧，用于引入非对称缺陷，增大结构双折射，实现保偏功能；两个小圆形空气孔对称设置在两个椭圆空气孔与中心的大圆形空气孔之间，用于进一步减小模场与基底材料的重叠度，降低损耗；包层包括与纤芯同轴的保护层，保护层通过呈辐射状的支撑条与纤芯相连，保护层和支撑条均为基底材料。

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Abstract ：

报道了一种基于光谱合束的Nd:YAG固体激光器双波长光源。系统由两个固体Nd:YAG脉冲激光器通过光谱合束组合而成，两个固体Nd:YAG脉冲激光器可独立工作，有利于输出脉冲的波长调谐、功率调节和相对延迟调整。通过光栅的色散特性以及输出镜的共同外腔反馈将各个激光器锁定在不同波长，从而实现合束，获得的激光源中心波长锁定在1 061.5 nm和1 064.6 nm，两谱线中心间距为3.1 nm，组合光束的输出能量为173 mJ，组合光束的光束质量因子M~2为2.8×2.2；两个Nd:YAG激光器独立工作的输出能量分别为94 mJ和92 mJ，在合束方向上的光束质量因子M~2分别为2.7和2.1，在非合束方向上的光束质量因子M~2分别为2.2和1.9；组合光束的输出能量为两个Nd:YAG激光器能量总和的93%，组合光束的光束质量因子与单个Nd:YAG激光束的光束质量因子M~2基本相同。该双波长激光源满足波长间隔小、输出功率大小相近、同光轴等要求，在太赫兹波产生、测速激光雷达以及医疗仪器等应用领域具有重要作用。

Keyword ：

光谱合束 光束质量 Nd:YAG激光器 双波长 输出能量

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Abstract ：

Terahertz waves possess remarkable penetrability, capable of passing through a wide range of non-metallic, nonpolar materials without causing ionization. This unique characteristic makes them particularly useful in the field of computed tomography, enabling the capture of detailed external and internal structures of samples along their threedimensional absorption coefficient distributions. In this process, the sinogram for each vertical layer is generated through raster scanning at different projection angles. These sinograms are then transformed into sectional images using filtered back projection and other algorithms based on the Fourier central slicing theorem. As the field has developed, a diverse array of illumination modes, imaging configurations, and reconstruction algorithms have been proposed. These advancements serve to accommodate the development of terahertz imaging instruments and components, as well as the expanding range of application scenarios. This study reviews the principals of terahertz computed tomography. We provide a comprehensive review of its recent research progress, focusing on enhancing three key areas: reconstruction quality, imaging resolution enhancement, and data acquisition efficiency. © 2024 Universitat zu Koln. All rights reserved.

Keyword ：

illumination field manipulation three-dimensional imaging terahertz imaging computational tomography

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Abstract ：

太赫兹波作为一种穿透性强、具有非电离性和惧水性的电磁波，可以穿透多种非金属、非极性介质材料。太赫兹计算层析成像技术基于傅里叶中心切片定理和直线传播模型，通过记录不同投影角度下的强度数据，采用滤波反投影等重建算法获得样品三维吸收系数分布和内外部结构信息分布。随着太赫兹成像器件的不断发展和应用场景的拓展，已发展出多种照明模式、成像光路和重建算法，并已在文物保护、骨密度测量和无损检测领域开展了应用探索。概述太赫兹计算层析技术的基本原理，并从提高重建质量、分辨率和采集效率三方面具体介绍太赫兹计算层析成像技术的最新研究。

Keyword ：

照明光场调控 三维成像 太赫兹成像 计算层析

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Abstract ：

本申请提供了，一种器件结构、太赫兹波调制器、通信装置和制备方法，该结构包括基底和M×N个调制单元，其中：基底包括第一层和第二层，第一层中设置有栅体，栅体包括M×N个孔洞，第二层覆盖于第一层之上，M和N为正整数；M×N个调制单元设置于第二层之上，M×N个调制单元的位置与M×N个孔洞的位置一一对应，每个调制单元包括由下到上依次设置的第三层和第四层，第三层包括导热材料，第四层包括二氧化钒材料。通过加入包括微栅结构的基底，以对调制单元进行支撑，从而能够提高器件结构的稳定性，并实现太赫兹波的面阵控制。

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Abstract ：

本发明公开了一种基于智能区块链分片的工业互联网性能提升方法，属于通信网络技术领域；本发明采用基于信誉机制的区块链智能分片和自适应共识协议切换方法，在大幅提升区块链系统可扩展性的同时，可有效保护其安全性和去中心化。此外，本发明引入了云边端协同计算为分片区块链提供算力支持，并采用并行计算卸载和太赫兹通信技术来增强云边端三层网络之间的协同性。最后，本发明将优化问题建模为马尔可夫决策过程，并采用近端策略优化算法进行求解。仿真结果表明，本方法的系统总延迟与区块链交易吞吐量均优于其他方法。

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Abstract ：

基于预群聚结构的多注TM31模太赫兹扩展互作用速调管高频结构，属于太赫兹技术领域。包括外壳、电子枪阴极、聚束腔和输入与输出端口。该太赫兹扩展互作用速调管高频结构的外壳用于保护其内部结构，电子枪阴极设置在外壳开口的一侧，用于发射多电子注。高频结构设置在外壳内部包裹的真空结构中，输入与输出端口设置在外壳上，用于输出太赫兹辐射。本发明解决了真空电子器件向太赫兹波段发展时所面临的互作用效率低和输出功率不足的难题，同时增大了太赫兹频段器件的尺寸，有利于工程制管的加工和高功率太赫兹源的实现。

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Abstract ：

Terahertz (THz) in-line digital holography is a promising full-field, lens-free, and quantitative phase-contrast imaging method with an extremely compact and stable optical configuration. Hence, it is suitable for the application of THz waves. However, the inherent twin-image problem can impair the quality of its reconstructions. In this study, a novel learning-based iterative phase retrieval algorithm, termed as physics-enhanced deep neural network (PhysenNet), is introduced. This method combines a physical model with a convolutional neural network to mitigate the twin-image issue in THz waves. Notably, PhysenNet can reconstruct the complex fields of a sample with high fidelity from just a single in-line digital hologram, without the need for constraints or a pre-training labeled dataset. Based on simulations and experimental results, it is evident that PhysenNet surpasses existing phase retrieval algorithms in imaging quality, further enhancing the application range of THz in-line digital holography. © 2023 Universitat zu Koln. All rights reserved.

Keyword ：

in-line digital holography phase retrieval continuous-wave terahertz neural network

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Abstract ：

Ceramic matrix composites (CMC) have a series of advantages such as low density and high temperature resistance, and are widely used in components such as the leading edge of aircraft wings and advanced gas turbine engines. Due to factors such as diversified manufacturing processes and complicated manufacturing steps in the production process, defects inevitably remain in the material, which has a non-negligible impact on the stability and reliability of the material. In response to the urgent need for internal defect detection, based on the advantages of rich information and high time resolution of terahertz time-domain spectroscopy (THz-TDS) technology, a terahertz detection method for non-destructive detection of internal defects of CMC is proposed. First, the reflective THz-TDS system is used to perform non-contact non-destructive testing on the prefabricated CMC sample, and point-by-point scanning detection signals are obtained in the sample. Then, in view of the obvious phase delay phenomenon that often occurs in the high-frequency signal after high-order filtering, a zero-phase filtering method is proposed, which eliminates the phase delay and accurately extracts information such as peak value, phase and time-of-flight. On this basis, the multi-feature weighted fusion imaging method is used to draw the two-dimensional surface imaging results of the material defect, and the corresponding three-dimensional defect topography is reconstructed, and the defect topography position information is visually displayed, and the location and quantitative evaluation of the defects in the CMC sample are achieved. © 2023 Editorial Office of Chinese Journal of Mechanical Engineering. All rights reserved.

Keyword ：

zero phase filtering ceramic matrix composite fusion imaging terahertz spectroscopy defect detection

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