Author Affiliations
Abstract
National Key Laboratory of Microwave Photonics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
An approach for frequency division of an optical pulse train (OPT) based on an optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. When the OPT is injected into the OEO, a microwave signal with a frequency equaling fractional multiples of the repetition rate of the OPT is generated. This signal is then fed back to the OEO, maintaining its oscillation, while simultaneously serving as the control signal of a Mach–Zehnder modulator (MZM) in the OEO. The MZM acts as an optical switch, permitting specific pulses to pass through while blocking others. As a result, the repetition rate of the OPT is manipulated. A proof-of-concept experiment is carried out. Frequency division factors of 2 and 3 are successfully achieved. The phase noises of the OPT before and after the frequency division are investigated. Compared to previously reported systems, no external microwave source and sophisticated synchronization structure are needed.
frequency division optoelectronic oscillator mode-locked laser microwave photonics Chinese Optics Letters
2024, 22(4): 043902
郑州西亚斯学院计算机与软件工程学院, 郑州 451000
针对现有的基于CNN的方法存在特征信息丢失、杂波信息干扰严重、忽略了不同尺度特征之间的相关性、需要大量训练样本等问题, 提出了一种基于孪生特征引导多尺度网络(SFGMSN)的坦克检测方法。在SFGMSN方法中, 设计一种改进的Inception模块, 提取坦克目标图像的多尺度特征, 并进行特征融合, 更好地恢复了坦克目标的精细分段信息; 为了提高目标区域的特征感知能力和抑制背景干扰, 设计了一种局部通道注意机制(LCA-M), 得到更加精准的检测结果; 最后, 利用元学习器检测坦克目标。SFGMSN方法充分利用多尺度卷积、空洞卷积、孪生网络、局部通道注意机制和元学习器的优势, 能够解决传统CNN模型过度依赖大量训练样本以及在小样本条件下可能出现的准确率低和泛化性差的问题。在坦克图像数据库中进行实验, 结果表明, 所提方法具有较好的检测效果, 平均检测精度为90.12%, 可实现复杂场景下坦克检测, 对低分辨率坦克图像具有很好的鲁棒性。
坦克检测 孪生网络 多尺度CNN 元学习器 孪生特征引导多尺度网络(SFGMSN) tank detection Siamese network multi-scale CNN meta-learner Siamese Feature-Guided Multi-Scale Network (SFGMSN
强激光与粒子束
2023, 35(11): 111001
Author Affiliations
Abstract
1 Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
2 Laser Fusion Research Center, China Academy of Engineering Physics, Mianyang, Sichuan 621900, China
3 HEDPS, Center for Applied Physics and Technology, and College of Engineering, Peking University, Beijing 100871, China
The first laser–plasma interaction experiment using lasers of eight beams grouped into one octad has been conducted on the Shenguang Octopus facility. Although each beam intensity is below its individual threshold for stimulated Brillouin backscattering (SBS), collective behaviors are excited to enhance the octad SBS. In particular, when two-color/cone lasers with wavelength separation 0.3 nm are used, the backward SBS reflectivities show novel behavior in which beams of longer wavelength achieve higher SBS gain. This property of SBS can be attributed to the rotation of the wave vectors of common ion acoustic waves due to the competition of detunings between geometrical angle and wavelength separation. This mechanism is confirmed using massively parallel supercomputer simulations with the three-dimensional laser–plasma interaction code LAP3D.
Matter and Radiation at Extremes
2023, 8(5): 055602
1 中国工程物理研究院激光聚变研究中心,四川 绵阳 621900
2 中国工程物理研究院研究生院,北京 100088
靶点激光焦斑的偏振匀滑是激光聚变驱动器的关键技术。建立数学模型,对会聚光束中的偏振匀滑进行理论分析。指出该技术在光束远场纵向的匀滑效果,推导激光远场横向分离量和纵向分离量分别与偏振匀滑晶体厚度和倾斜角度的关系。通过数值模拟,给出了激光远场焦斑形态参数与晶体参数之间的关系曲线。结果表明,当晶体厚度和偏转角度取特定范围时,焦斑可以得到最佳的匀滑效果。
激光聚变装置 惯性约束聚变 偏振匀滑 焦斑整形 会聚光束 光学学报
2023, 43(20): 2014001
1 福建江夏学院钙钛矿绿色应用福建省高校重点实验室, 福州 350108
2 福州大学物理与信息工程学院, 福州 350108
3 闽江学院福建省海洋传感功能材料重点实验室, 福州 350108
4 福建省计量科学研究院国家光伏产业计量测试中心, 福州 350003
本文采用简单的室温球磨法制备了一系列L-组氨酸(L-His)和5-氨基戊酸(5-Ava)修饰的Cs3Cu2I5钙钛矿荧光粉, 并对Cs3Cu2I5∶x%L-His和Cs3Cu2I5∶x%5-Ava(x=0、0.5、1、1.5、2)样品的物相、形貌、光学和稳定性进行了分析。氨基酸添加未对Cs3Cu2I5钙钛矿的晶体结构造成影响, Cs3Cu2I5仍属于Pnma空间群, 但氨基酸的加入对钙钛矿的晶粒尺寸有一定的限制作用, 并有效改善了其光电性能。当x=1时, 经L-His和5-Ava修饰的Cs3Cu2I5钙钛矿较纯Cs3Cu2I5钙钛矿的荧光强度分别提升约1.30倍和1.41倍, 光致发光量子产率(PLQY)提高约25.09个百分点和30.47个百分点, 荧光寿命有效延长。研究发现, 性能的改善与氨基酸中氨基以及羧基基团的作用有关, 氨基以及羧基基团钝化了钙钛矿的缺陷并抑制非辐射复合过程的能量损失。此外, 采用L-His和5-Ava修饰的Cs3Cu2I5钙钛矿荧光粉制备了蓝光发光二极管(LED), 在70 mA的偏流下, 该LED光效率较纯Cs3Cu2I5器件分别增强达1.85倍和2.10倍, 表明这类材料在LED领域有着极大的应用价值。
钙钛矿荧光粉 氨基酸修饰 光致发光量子产率 缺陷 非辐射复合 perovskite phosphor Cs3Cu2I5 Cs3Cu2I5 amino acids modification PLQY defect non-radiative recombination
Author Affiliations
Abstract
1 Laser Fusion Research Center, China Academy of Engineering Physics, Mianyang 621900, China
2 Graduate School of China Academy of Engineering Physics, Beijing 100193, China
3 Key Laboratory of Optical Fiber Sensing and Communications, University of Electronic Science and Technology of China, Chengdu 611731, China
Matter and Radiation at Extremes
2023, 8(2): 029901
Author Affiliations
Abstract
1 Laser Fusion Research Center, China Academy of Engineering Physics, Mianyang 621900, China
2 Graduate School of China Academy of Engineering Physics, Beijing 100193, China
3 Key Laboratory of Optical Fiber Sensing and Communications, University of Electronic Science and Technology of China, Chengdu 611731, China
Broadband low-coherence light is considered to be an effective way to suppress laser plasma instability. Recent studies have demonstrated the ability of low-coherence laser facilities to reduce back-scattering during beam–target coupling. However, to ensure simultaneous low coherence and high energy, complex spectral modulation methods and amplification routes have to be adopted. In this work, we propose the use of a random fiber laser (RFL) as the seed source. The spectral features of this RFL can be carefully tailored to provide a good match with the gain characteristics of the laser amplification medium, thus enabling efficient amplification while maintaining low coherence. First, a theoretical model is constructed to give a comprehensive description of the output characteristics of the spectrum-tailored RFL, after which the designed RFL is experimentally realized as a seed source. Through precise pulse shaping and efficient regenerative amplification, a shaped random laser pulse output of 28 mJ is obtained, which is the first random laser system with megawatt-class peak power that is able to achieve low coherence and efficient spectrum-conformal regenerative amplification.
Matter and Radiation at Extremes
2023, 8(2): 025902